I've done a lot of reading on this subject, but I found no solution to the following problem. Obviously, if anyone can forward me to a similar thread, I'll be very appreciative.

I've bought this 2003 Audi A4 1.8t quttro three years ago. A real jewel. Never had a problem with it, took myself good care of it, but it has one gripe that I'm trying to solve since the day I bought it: cabin BOOM. Really disconfortable! I've had this since I bought it (I did not realized it then how annoying is going to be).

It does not happen on highway (that's why I love cruising it there). But city driving is a real pain. The entire cabin booms (resonates? no rattles though) when around 1100 rmp and 1900 rmp, and when going over bumps at low rmp. Going over bumps at high rmp does not create the cabin boom. To aggrevate the matter, this boom does not happen always, some days the car is cool and quiet regardless of rpm, although there is some slight vibrations felt in the cabin at those same rmp. Other days, though, the BOOM gremlin comes to life. I ended up thinking that it is a subjective matter, taking two advils always makes the cabin quieter. However, I could not notice that on cold days most of the time the cabin is at it should be: quiet. Hence, this is a bonus to compensate the friggin cold in Chicago. Summer came, and the BOOM is back.

Anyone? Solution?

My latest readings point me to exhaust (exhaust drone)? It feels that if it is at a certain "height", it resonates acoustically (or structurally), so going over bumps exhites those positions since exhaust shifts up and down.

I need to mention that the idle is absolutelly quiet, not even a bit of vibration (you can bet the engine is off). Car has 70k. Changing tires did not affect anything. Going over bumps has no relation to wether the front or back tires go to a road expansion joint in terms of the BOOM - absolutelly the same noise at the same intensity. Audi dealer sais "IT IS NORMAL". It cannot be normal.

I've also noted that the dual-exhaust pipes have some connecting rod with a screw in there. I was wondering if that can be used to adjust the distance between the pipes with a direct consequence on the resonance (acoustical tuning) or that is only for support? I am asking rather than trying since I don't have any means to getting under the car, but I can try to if anyone sais it could.

Thanks! Sorry for being too long

I would really really appreciate someone who can give me some hints ...

 

No help here, but I can relate to your problem. I hear the repetitive thud when I drive at lower speeds with the windows down or sunroof open. At first i thought it was from the tires, but like yourself, new tires had no effect.

 

so ur sayin when the windows are down or sunroof open u get a helicopter sound?

 

No, it is not the buffeting (helicopter like) sound you get when sunroof is open. As a matter of fact, windows up or down, sunroof closed or open, has NO effect on the boom. Ok, window down the boom is less noticeable because of the more wind-noise.

It is just a short-lived (on bumps, low speed, more pronounced on the 1100 and 1900 rpm) or continuous, around 50-100Hz sound that resonate throughout the cabin when rpm is 1100 and 1900 regardless of speed or gear. I should add that it sound stronger if not under load (decreasing speed) than on the acceleration gradient. It does not sound as if the exhaust is touching the body, it just ... sounds in my head, like my head is inside a drum. Cannot pinpoint the source, but seems to come from right under the car (center muffler?). It happes either if I drive or rev the engine in park. I bet is exhaust-related, but I don't know what to do to "shift" it a bit hopefully to change the resonant frequency.

So that's why I was wondering what that screw that connects the two exhaust pipes do ... can I tune the exhaust note from that? Should I change the exhaust tips?

Thanks