1997 540I strange noise any thoughts?

[Costick]

Ok so I had to take a 2 hr trip today in the rain and on the way back I noticed my exhaust was way louder than normal and when I would blip the throttle and let off the car would slow down really fast almost as though it had an exhaust brake. I got the car home crawled under it and no leaks, holes, loose things in on or around the exhaust. Also as strange as it is the car felt to have more power but could be my head going man that sounds bad ass and faster haha. Any thoughts?

[mattmartindrift]

check to see if the exhaust is sitting against the transmission cross member.

[stealth540i]

I have the same exact noise only when it rains. Not sure what it is but it sounds bad ass IMO. Makes it sound like I have a bad ass exhaust system, but only have an aftermarket muffler. Never had any issues with but love the sound. I asked a few friends about it, and they said it may be the cold rain water cooling the exhaust down, but I don't think that is it. Don't know, but love the sound.

[Costick]

Matt/will do
Stealth/I did the muffler and silencer delete and it sounds bad ass all the time but last night it was like I was running straight pipe but without the pop pop pop you would get after you let off the throttle in most cases. I am most worried though about the heavy slowdown when I would give it a good amount of throttle then lift off. Thanks for responding guys and hope to hear from more of you.

[mattmartindrift]

I have the same exact noise only when it rains. Not sure what it is but it sounds bad ass IMO. Makes it sound like I have a bad ass exhaust system, but only have an aftermarket muffler. Never had any issues with but love the sound. I asked a few friends about it, and they said it may be the cold rain water cooling the exhaust down, but I don't think that is it. Don't know, but love the sound.



mine did this through puddles. I found that the cooling of certain portions of the exhaust allowed it to flex just enough to contact the transmission cross member; thus causing the exhaust to resonate through the chassis. I'll admit it sounded interesting.

[stealth540i]

That sounds about right. I did notice a little rattle like the exhaust was touching the crossmember or something in that area. I have trans mounts to put in yet and I'll look at the exhaust mounts while I'm under there. But I must admit, I do love the extended exhaust note when this happens. I did the muffler delete and welded B&B triflo in place and the sound is amazing when this happens.

[Costick]

Thats it I am going to have my shop weld the exhaust to permanently sit on the transmission cross member! lol thanks again guys

[jamesdc4]

I think Matt is right.
The rubber grommet that suspends the exhaust (part #3) wears out over time and sags allowing the exhaust to touch the center support brace (part #5).
http://www.realoem.com/bmw/diagrams/m/l/20.png

http://i13.photobucket.com/albums/a282/jamesdc4/1106081441a.jpg?t=1262842592