Exhaust - loud low frequency resonance inside the cabin at low RPMs

[klem74]

I got my Stasis Coilovers and exhaust installed last week and while the coilovers are AWESOME the exhaust is loud and very annoying at low rpms inside the car cabin. It generates a very low frequency noise in the 2000 to 3200 rpm range. It sounds very nice on the outside. It gets a LOT quieter above 3500 which I really like.
It seems that the exhaust resonates with the cabin.

I bought it because I read very good reviews and that it is very quiet, like a semi luxury car should sound. I am hoping that this is an installation issue.

I drove 400 miles this weekend and had to keep car in 5th gear to keep the revs around 3500 rpms where the car cabin resonance fades away.

I am talking about a very gentle driving style, 80mph no sudden passing, constant speed.

The resonance is there when I slightly touch the throttle and also when I let go off the throttle (engine breaking). It is only ok when the car is going down the hill and there is no engine load.
The car radio was continuously adjusting its volume to compensate for the cabin noise.

When I floored the throttle on either 4th,5th or 6th gears around 3000rpm the low frequency resonance got so bad that it almost pops my ears. When I floored it at 4000 rpms it was nice and quiet but still noticeable.

Any suggestions will be greatly appreciated.

[pdxrunr]

which brand of exhaust do you have? I recently installed the APR exhaust and have experienced something similiar.

[Jason@STaSIS]

Probably something on the exhaust touching part of the car. Check the underside / clamps / routing of the exhaust.

You are probably hearing an exhaust clamp touching/vibrating on something.

[scoobycarolan]

yea, Jason's right on here. I'd go back to the shop and have them recheck everything.

[klem74]

Stasis catback. I called Stasis tech support and they say that it might be touching some part of the car and the vibration basicaly transfers over to the interior.
I also think that it gets louder as the exhaust comes up to the temperature (expands).

The salesman from Achtuning recomended to add a resonator which should make it quiter but then I'm affraid that i'll end upwith stock sound and very expensive exhaust tips.

The noise is definitely coming from the rear. When I looked around the mufflers, there is a lot less room to left of the left mufler (rear muffler has lot more space around it) and mabe as the exhaust expands it touches the sheet metal or some other part.

[EuroA4]

Do you have an avant or sedan?

[klem74]

Sedan

[Bryan]

mine stasis exhaust is no problem...it's very quite in cabin all the time...I WANT LOUDER !!!!! = ="

[DoThisMyWay]

Really? My Stasis exhaust is louder than I like but I have an Avant.

[klem74]

I guess every one of us differently defines the loud and the quiet. I just want be able to drive couple hundred miles at constant speed and not get a headache after first 50.

The car sounds awesome while I drive it in the city. Nice deep tone, but in the city, I hardly ever stay constant around 3000rpms and on 5th or 6th gear. The problem has much higher visibility on the expressway.

I had my shop inspect the installation and I also looked at it myself and found no metal-to-metal contact. It must be the air resonance somewhere underneath the car.

Bryan, so your setup does not have the low frequency drone at 2500-3200rpms on 5th or 6th while cruising at 80mph? Any chance to get some photos of the underneath of your car?

[AudiWxGuy]

Hey, I've got a STaSIS Exhaust as well...The drone you're hearing is not normal. I crusie at 80 on the highway on cruise control at 2600 RPM and it's very quiet in the car. If I acclerate in 5th or 6th gear at low RPM's i get a little drone...but I got that with the stock exhaust as well. I'll tell you the only time the drone is pretty bad is when you're in too high a gear at too low an RPM. Like when I do 50 mph in 6th i get some drone. However, since my exhaust has broken in, that's gotten less noticeable as well. I think you may want to have yours looked at again...I think what you're hearing is not normal.

Also...how much did the Coil Overs improve the handling? and how is the ride? I just bought a set and am stoked to have them installed. I hate my 4x4 suspension I have now.

[klem74]

Thx a lot. The install is almost perfect. The shop owner and I took a lot of time to verify it.

I am wondering if the distances between the exhaust pipes, mufflers and the car’s exhaust cavity differ between our cars. Different distance might affect or introduce some resonant frequencies. I also wonder about the tip position and resonance with the rear bumper interior. Any ideas? This is why I wanted to see some pics of other cars that do not have the same issue.

I also wonder if I might have received a faulty exhaust.

The coilovers are simply AWESOME!!! I got my car bit too low for my taste 25.5 all around. Planning on going 26.0" front and 25.75 rear (I purchased spacers for the rear) due to the fact that rear fender is actually lower than the front one.
My previous car was a B6 S4 and did feel stiffer around the corners (S4 sway bars) than A4 with Stasis SS. However I prefer my current setup over the S4. The Street Sports give you a very good comfort level, so if you are the person who does not race on the track then I think these are perfect. I recently drove from Chicago to Kentucky (approx 900 miles total trip), 3 people in the car, full trunk and no complaints from my wife as far as the ride comfort.

[klem74]

I should also add that even with stock A4 sway bars my car's handling and cornering with Stasis SS improved dramatically. The small bumps are nicely attenuated and quickly recovered from (great job Stasis and KONI) and once you hit the corner the suspension stiffens and the body roll is significantly eliminated. If I get the sway bar(s) the car should handle just like an S4 if not better (lower front mass) but still be more comfortable on the easy daily driving. Best of both worlds. Hope this helps.

[AudiWxGuy]

Just what I was looking for! Thanks!

[klem74]

Ok, so I went to the recommened by Stasis car shop in my area and the owner took it for a ride. He did not find anything wrong. So it looks like it was me being too picky I guess. It must be normal for these free flowing mufflers to drone at 3000 rpms.
I will have to find a way to attenuate the car so it does not propagate to the interior as much or will be forced to sell this exhaust and go stock w/o the resonator. I just cannot live with not being able to comfortably cruise at 80mph.
I actually took a sound level measurement inside the car and here is what I got:
Parked: 68dB
Started, idle: 82dB
accellerating at 2500rpms: 102dB
accelerating at 4000rpms: 88dB
(for thouse not familiar with dBs: 6dB increase = 2x of sound level, 12dB = 4x and so on) The interior of the car is 14dB (5 times) louder at 2500rpms than at 4000rpms.

Bottom line, I must be more sensitive than most people and probably should have done more research before going with an aftermarket exhaust.

[AudiWxGuy]

I don't know man, my car is real quiet when doing a steady 80 mph. Give the exhaust a chance to break in a bit.

[klem74]

Is your car chipped. I think I am one of the very few people who did exhaust before the ECU mod. I wonder if the different boost profile on the stock ECU at low rpms causes my problem.

Other than that the exhaust sounds very nice. SS Coils are awesome!

[AudiWxGuy]

Not chipped. I was, but didn't think it was worth after a little while. So I got flashed back to stock, got my money back and got the exhaust instead. Plus, I've heard that being chipped and not having an exhaust with bigger pipes creates a lot of backpressure that isn't really good for the engine. If I do get chipped again it's probably going to be with GIAC.

[FastB7S4]

We have the same problem with exhausts on S4's except that ours drone a little between 1-2k rpm (mostly around 1500) which is cruising speed of 45-50. Everyone says this is normal. It's not terrible, though, and definitely tolerable.