[MBlaster]

I have a 2015 M235i with an AA axle back exhaust and a BM3 Stage 1 map, 68k miles. I’ve been noticing a knocking sound that was heard intermittently no mater what drive mode or in park or drive. When I installed the exhaust, I had very little space between the tail pipe and the rear bumper cutout so, I made some adjustments and increased the spacing. This made some definite improvements and eliminated most of the knocking. There’s still a little knocking but, it’s not nearly as often and only occurs in drive or reverse and not all the time. It also sounds different compared to the sound from the exhaust pipe knocking on the plastic bumper. I backed it up on your ramps and crawled under there to see if I could find something else and noticed the exhaust pipe where it flattens out and squeezes between the bottom of the chassis and a welded aluminum brace is almost setting on the aluminum brace, maybe 1/16” separation. This separation may be reduced due to the addition of a he AA exhaust requiring the stock exhaust to be cut out. What was originally a solid welded pipe all the way back now has a coupling which may allow for some sag. I’m attempting to attach a photo for reference. Any opinions or advice or anyone else experienced this before?

[ClassicWill]

Is this a convertible model? If so I had an AWE axle back installed on my m235i convertible. But the under-body brace on the convertible slightly touched the exhaust. I went to AutoZone and got this adhesive wrap that cushioned the gap and the rattle is gone when the car gets warmed up. Hope this helps.

[MBlaster]

It’s not a convertible. I was thinking of using some type of high temp wrap but, had no experience with them or where to find them. Looks like I’ll be heading to AZ this weekend. Thx

[MBlaster]

Thanks Classicwilly, the exhaust wrap material between the exhaust pipe and bracket worked. Now I’m on to tracking that annoying squeak.