[RedlineTuning]

I put on the AKRA Evolution recently... I also put on the Macht Snell Stage 2 filter/duct at the same time. I immediately noticed the engine sound coming back through the intake from 3-4K on my first drive (a loud raspy rattle/exhaust type sound that seems to be coming from right in front of the driver). I spent a good day trying to figure out if I had tightened down everything properly thinking it was an exhaust leak. But under full throttle, the sound would only happen from 3-4K - if it was a leak I would heard a sound across the RPM band... Being that I work as an air induction designer for Ford Motor Co., I started wondering whether the sound was actually engine noise transmitting back through the intake. We put resonators on the air induction path of every engine made to cancel out unwanted engine frequencies - there aren't any on the M3 and this is my guess as to the problem. The smaller original inlet helped squelch some of the sound, along with the more restrictive exhaust. Now that air flow is much improved, the sound is very noticable.

I then removed my new duct/filter from Macht Snell, put back on the stock filter and more restrictive duct to the intake - the sound was muted and definitely a bit quieter. Unfortunately, I could not take the loss of power and immediately put it back on. The only real test I didn't want to undertake was swapping the exhaust back to stock to really take a listen. So... I'm living with it, and I appear to be the only one in the car who notices it...

Originally Posted by stefanos-ktm

I have take the same exhaust(pictures here http://www.m3post.com/forums/showthread.php?t=435942 ) with yours 1 week ago. it does the same noise in the same rpm dont worry. OR BOTH we have a problem