Hi all, new Audi owner here, just bought a used 2011 S4 with automatic transmission. For the past several years I've driven a Silverado in the winter and a highly modified Mustang Cobra in the summer but needed to save some money so the S4 seemed like a great year-round combination of the two vehicles. I did a lot of experimenting with exhausts on the truck and the Cobra and love the deep sound of the V8 but hated the booming drone that always seemed to show up right in the rpm range you use most. The S4 exhaust is way too quiet even for me and I've read a lot of posts here on various exhausts, and drone and rasp seem to be the two things that a lot of people try to eliminate.

Here are some things that I learned from the Silverado exhaust experiments that might help us with the S4's.

First exhaust was a Flowmaster catback. Too loud and droned. Replaced with a Magnaflow catback. Different sound, same drone. Added a Vibrant straight-through perforated resonator between the cats and muffler, no improvement. (The Magnaflow muffler that came with the system was also a straight-through perforated design, same as the two small stock resonators near the S4 downpipes.) Did some research and found that Dynatech makes these cone-shaped "Vortex cones", which are supposed to reduce the sound volume by 2-4 dB (I did a lot of dB measurement with a phone app as part of these experiments). I tried the cone in 3 places: at the junction where the two cat pipes merged into a single straight pipe that went back to the muffler; at the end of the muffler; and just before the exhaust tip. No difference in any of these locations. Next I tried an auger-style insert from Summit Racing. This was basically a pipe about 1 inch diameter that had 3 discs welded onto it as baffles; each disc had a split and a twist so exhaust could get past it. The diameter of the auger discs was the same as the inside diameter of the pipe. I put the auger into the straight part of the exhaust pipe just after the merging of the two cat pipes and got no difference. HOWEVER when I put it into the exhaust just behind the muffler there was a HUGE difference; so much different that I cut off one of the discs to make it louder. This location also happened to be right before a 45 degree bend in the piping. I suspect that the auger baffles reflected some sound waves back into the muffler's perforated core at angles, so that the perforation could absorb some of the sound energy; and that it also scattered the sound waves so they could not set up a vibration in the piping and cause the booming sound. Just a guess. I did all this with band clamps so I could try different setups so it looked like spaghetti when it was done but it sounded perfect.

I did notice some heat buildup where the auger restricted flow, so I drilled some holes into the discs (not in line with each other) to reduce restriction and it didn't affect the sound. Drove it like that for probably 10,000 miles with no problems.

So those of you that don't like the drone of your exhaust setup, maybe an auger insert slipped into the pipe just after a straight-through perforated muffler or resonator will help. The auger was really cheap, maybe $20.

Good luck if anybody tries it, I'd like to make the stock exhaust deeper and a TEENY bit louder with no drone and no rasp and am thinking about the resonated X-pipe that a lot of you have written about in other threads.