I have an 05 s4 the car makes a winning noise as I accelarate it sounds as if the car has a supercharger. The only mods the car has is flowmaster mufflers in the rear and an a k&n drop in filter. The car also has a dead spot when you accelarate, almost as if It had turbo lag you give it gas then within seconds you feel the power quick in.One last thing I noticed is the exhaust sounds like its fluttering, again I only replaced the rear muffler section (2.25 in and out) on the rear on the inlet of the muffler the pipe is slightly crushed due to the angle the muffler shop had to do to adapt the muffler with stock pipes. The motor runs straight no check engine light. What do you guys think? By the way a friend k&n filter that lack of oil can produce the winning noise. By the way a friend of mine said that lack of oil on the k&n filter can cause for the whining noise.

 

I have an 04 S4 and I have the whine as well. Mind you I am not expert, but I do know that when Audi put a V8 in the space of a 4 cylinder they had to get creative. The timing chain is behind the engine, not the front, near the firewall, and that is the whine you hear. The other stuff I do not know, except that some Audi mufflers have a valve that opens up or closes after a certain rpm, I can't remember to give the nice rumble at low speeds and smooths out when you are just cruising above some certain rpm. They discontinued the use of these mufflers after a certain time for whatever reason.