Some thoughts and problem on HKS Full Dual Muffler Exhaust

[Suzuyabot]

Had the HKS exhaust installed last December, took it for over 2k miles. The both sound modes are perfect for people who want an exhaust for different purposes, or sometimes when I have different moods in my car(although it's not as convenient as those valves).
As I turned off the ASE and with the caps on(silent mode), the car is quiet as f. The only noise I hear is the road(the shitty road in Portland OR area). And it's huge difference in the cabin compared to the aggressive mode.
The sound from outside does not differ very much, you do hear the difference after releasing your throttle, the difference is more on the air going through the exhaust. The tubes you place another tube or cap on is more like a resonator, I assume.
But for the sound overall, it's great. The bass of the sound coming out is stronger and not that loud to make it unbearable, but still gives a very high quality texture of the sound, I love that point of these Japanese companies that they don't just make the sound LOUD. Same as the drone, from what I hear from the driver seat without windows open, the sound is OK. And I love the feeling that I hear how many rpm my engine is when I accelerate. So the aggressive mode is already perfect, and the silent mode is even more comfortable, even making you feel you are driving a Sentra.

This is the cold start during winter with aggressive mode.

This is just slightly revs right after the installation.










And there is a problem caused by the exhaust installation, I haven't resolve this problem and still trying to find out the reason. So you should expect to have an rpm area where the drone is coming out very strong. Mine is around 1300-1500 rpm. This drone is emphasized in aggressive mode and it's unbearable when it's cold starting or it's climbing up a hill. It's not just noise but you can feel your head is shaking and pressure attacking your ears(more like the whole car is vibrating). Although it's much much better in silent mode. But here comes the main part: There is metal sound during that drone. I don't know which part is causing this sound but it always come with the drone, and it sounds like coming from the rear back area(you can hear from the video, it's something vibrating). Brought my car back to the shop and they said they didn't find any touch point on the exhaust. So yea just to share this and see if there is any answer that might help me, because without this only problem, this is the perfect exhaust for me.

BTW, I was planning to record some sound with a proper microphone since the iphone's mic does not really showing the quality(although it's always the best to hear the sound by person). So if I do I will just update them here.

 

[VR30Infection]

Man. That doesn’t seem right. I hope others that have this exhaust can chime in and let you know if they experience the same issue. Maybe talk to HKS ?

 

[rvlbrs]

I have the same exhaust and have zeros issues like this. My guess is something is not right with how it's installed. If you have a metal on metal noise combined with drone, my guess it that it's not positioned correctly or leaning on something.

 

[Suzuyabot]

I have the same exhaust and have zeros issues like this. My guess is something is not right with how it's installed. If you have a metal on metal noise combined with drone, my guess it that it's not positioned correctly or leaning on something.

What is weird is that I did take the car back to shop and let them check for everything and they said there are plenty of space between exhaust and other parts. So I don't know if that's something else but caused by the vibration when it's droning. But I'm not sure if that drone is normal or not so yea I might go to a different shop or even back to dealership and ask them about it since people from my dealership are very nice and open about the modification.

 

[Suzuyabot]

Maybe talk to HKS ?

That might be a good option. Gonna try it if I can get contact with anyone from HKS US maybe.

 

[staying_tuned]

I’d take a rubber mallet and tap the entire length of the exhaust from underneath, I bet you find your culprit. The audio is challenging to parse with older ears but it almost sounds like a nut that made its way into the system or a loose slip joint that causes a racket at a particular RPM threshold that happens to coincide with the mellow drone you’d expect. When the shop double-checked did you physically see them lift and inspect?

 

[Suzuyabot]

I’d take a rubber mallet and tap the entire length of the exhaust from underneath, I bet you find your culprit. The audio is challenging to parse with older ears but it almost sounds like a nut that made its way into the system or a loose slip joint that causes a racket at a particular RPM threshold that happens to coincide with the mellow drone you’d expect. When the shop double-checked did you physically see them lift and inspect?

That was the thing I wasn't pay attention, and I'm now concerning about the trust issue on that. I only saw them taking the car into workspace and life up but then just sitting in another room and waiting. I think I need another inspection for real.

 

[Suzuyabot]

Well I did the cap switch at the shop since I was moving and got no tools to do it myself(they asked me for 160 for 1 hour labor wtf). And was trying to switch the tubes back to check the noise and found that the bolts aren't even the same. Kinda losing my last trust...

 

[Hernandooo]

holy rust batman!

 

[staying_tuned]

If possible pick up a set of race ramps to back onto, that will give you gobs of access to troubleshoot the rear. For the $160 in labor they charged you to simply allow you to work on the rear of your own car you could cover 2 sets of great off-brand “race” ramps. You should maybe do this regardless so you can get under the car quickly & easily if needed. You mention having no tools, gotta at least get a basic multi-tool set if modding so you aren't beholden to some $hit show shop when things like this come up. For certain they had no idea just how special an exhaust like this is and are likely used to mangling $300 ebay knock-offs. Just catch a good sale on a mediocre craftsman/kobalt etc. 200+ pc. general set for under $150. Father's day timeframe always seems to be the time to get $200+ tool sets for $99 at most of the big box stores. No excuse there really, just get it done so when you ask these things we can all help get after it and get you squared away in the future!

No need to contact your old shop ever again. Fortunately it’s just an exhaust so you can walk away and any competent shop can pick up on it to help. Don’t fret the mismatching bolt. Janky for sure and my OCD would bother me but you can pick up a few nice stainless steel nuts and bolts at any auto parts store. Just walk in with the one HKS nut & bolt you have and match them from a diameter standpoint. Nut/bolt design don't matter much for this application as long as your stainless. I had their ultra similar dual helmholtz style legamax on my Q60 (near identical motor to ours), here is a playlist I had created. Some very close and you'll hear no such rattles. Here is the install post. I ran the caps for about 3 months and decided it was too quiet and never put them on again and that was with high-flow catted downpipes so if your biased towards the more aggressive sound just leave em off, it's inevitable you will one day and right now it just serves to complicate your trouble-shooting.

Until you have some basics to trouble-shoot these kinds of things find another shop and tell them you have a rattle post exhaust install that you cannot hunt down. This is such a trivial issue that it isn't even worth time relaying much backstory other than you can't find the source of the rattle post exhaust install and you don't have access to a lift. They’ll have dealt with it hundreds of times, if not more.

@Hernandooo pretty certain that's just surface rust if you look closely. Plenty of 20+ y/o 4G63s running HKS bumper to bumper still in the wild hah, their stuff is pretty bulletproof. Even their silicon couplers on cold-side piping stays supple for decades with basic care. Bonkers quality for something that is fairly mass produced.

 

[Thefunk]

The way I deal with droning on the highway at least is just downshift. Like if I'm cruising at 60mph in 9th gear the drone is strong so I downshift to 7th and the drone is gone. This method will slightly increase fuel consumption due to higher rpm but at least it's more comfortable to hear.

 

[FSUZ33]

The metallic sound could be an internal piece/baffle(?) that wasn't welded properly and is vibrating.

You said you turned ASE off. Did you also turn off the noise cancellation? Not sure if those are connected or separate. It's possible that noise cancellation is picking up something and spitting out an annoying frequency to try to cancel it out. I really have no clue, just speculation.

Regarding the two pics of the bolts...
The bolt in the bottom pic appears to be the one that was made for that clamp. Can't say if that's the original nut, but both appear to be stainless.
I'm guessing the top pic is the bolt AND nut they lost/replaced. That bolt is zinc plated, not stainless. Judging by the rust present elsewhere that bolt could be permanent before you know it. The nut appears stainless, but it also looks like a nylock, and if the nylon melts out of it, it's more likely to loosen up causing you to chase another clanking noise. I'd replace both bolt and nut on that side.

 

[Suzuyabot]

If possible pick up a set of race ramps to back onto, that will give you gobs of access to troubleshoot the rear. For the $160 in labor they charged you to simply allow you to work on the rear of your own car you could cover 2 sets of great off-brand “race” ramps. You should maybe do this regardless so you can get under the car quickly & easily if needed. You mention having no tools, gotta at least get a basic multi-tool set if modding so you aren't beholden to some $hit show shop when things like this come up. For certain they had no idea just how special an exhaust like this is and are likely used to mangling $300 ebay knock-offs. Just catch a good sale on a mediocre craftsman/kobalt etc. 200+ pc. general set for under $150. Father's day timeframe always seems to be the time to get $200+ tool sets for $99 at most of the big box stores. No excuse there really, just get it done so when you ask these things we can all help get after it and get you squared away in the future!

No need to contact your old shop ever again. Fortunately it’s just an exhaust so you can walk away and any competent shop can pick up on it to help. Don’t fret the mismatching bolt. Janky for sure and my OCD would bother me but you can pick up a few nice stainless steel nuts and bolts at any auto parts store. Just walk in with the one HKS nut & bolt you have and match them from a diameter standpoint. Nut/bolt design don't matter much for this application as long as your stainless. I had their ultra similar dual helmholtz style legamax on my Q60 (near identical motor to ours), here is a playlist I had created. Some very close and you'll hear no such rattles. Here is the install post. I ran the caps for about 3 months and decided it was too quiet and never put them on again and that was with high-flow catted downpipes so if your biased towards the more aggressive sound just leave em off, it's inevitable you will one day and right now it just serves to complicate your trouble-shooting.

Until you have some basics to trouble-shoot these kinds of things find another shop and tell them you have a rattle post exhaust install that you cannot hunt down. This is such a trivial issue that it isn't even worth time relaying much backstory other than you can't find the source of the rattle post exhaust install and you don't have access to a lift. They’ll have dealt with it hundreds of times, if not more.

@Hernandooo pretty certain that's just surface rust if you look closely. Plenty of 20+ y/o 4G63s running HKS bumper to bumper still in the wild hah, their stuff is pretty bulletproof. Even their silicon couplers on cold-side piping stays supple for decades with basic care. Bonkers quality for something that is fairly mass produced.

Thanks for the very long reply! That was a lot!
For the tool I have a whole set for what I need right now, just at that time my things were all on the truck to my new home so I couldn't get them. But now I already got them so no worry for that, just changed the caps to tubes yesterday to check for the noises. To be honest, the best option for me is to find another shop with a good reputation. Although the one I went to is one of most reputable shop for tuning, maybe just a different specialty.

 

[Suzuyabot]

The metallic sound could be an internal piece/baffle(?) that wasn't welded properly and is vibrating.

You said you turned ASE off. Did you also turn off the noise cancellation? Not sure if those are connected or separate. It's possible that noise cancellation is picking up something and spitting out an annoying frequency to try to cancel it out. I really have no clue, just speculation.

Regarding the two pics of the bolts...
The bolt in the bottom pic appears to be the one that was made for that clamp. Can't say if that's the original nut, but both appear to be stainless.
I'm guessing the top pic is the bolt AND nut they lost/replaced. That bolt is zinc plated, not stainless. Judging by the rust present elsewhere that bolt could be permanent before you know it. The nut appears stainless, but it also looks like a nylock, and if the nylon melts out of it, it's more likely to loosen up causing you to chase another clanking noise. I'd replace both bolt and nut on that side.

I have the noise cancellation still on, and I did think about there might be some problem when the speakers are trying to cancel the noise from the exhaust. But I'm not sure if it will cause the metal sound though. I rechecked and can confirm that the bolt form the bottom picture with the cap on is the original bolt sent with the exhaust, so yea it should be some replacement, and that's nylock. So I'm gonna look a set of the same bolt and nuts and place them on.