135i OE axle-back rattle and low rpm fart?

[Thirdkelley]

Hey guys, I have an 08' 135i and has berk race (catless-non resonated mids), VRSF catless DPs, and stock axleback. This setup sounds great at WOT, however at low end, around 1800-2000 rpms when accelerating I get this deep/low tone fart sound. I hear this is normal, but just thought I'd put it out there.

My biggest problem is starting and revving...When I start the car, there is this rattle coming from the exhaust. It seems to apparent to be wastegate....and I can never rev the engine because this rattle overpowers the exhaust tone. My mechanic thinks I could have a broken muffler baffle, I also think it could possibly be the exhaust flap? (I've tried golf tee mod and sounds the same. Its not a consistent rattle, it only presents itself when starting or revving really. Could it be the stock axle-back being restrictive to the 100% free flowing mids and DPs? Just throwing thoughts out there....if people want me to post a video, I'd be happy to.

[Trptguy]

I have this too but I have an afe exhaust that is brand new, it was doing it with stock exhaust also. I think it is something else

[e36addict]

Post a vid. Got me curious.. there aren't really any baffles in the muffler that could come loose

[DietTab]

I get it sometimes, pretty sure its from the two downpipes rattling against each other at their flanges.

[JimUlrich135]

Either waste gate or rear muffler flap.

[Trptguy]

If it was the waste gate wouldn't the sound always be there and not only when you rev it?
Also I tried pulling the vacuum hoses and it did nothing so I don't think this is a waste gate issue.

Down pipes rubbing makes more sense. Is there a fix for that?

[DietTab]

Loosen the v bands and clock them a little differently so they have more space. I'm probably going to trim the flanges a little and put a piece of sound deadener between them so they can't make noise anymore