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      03-09-2021, 04:11 PM   #1
Filip3615
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Bmw 435i rattle from rear on cold start, exhaust or other component?

Hi guys, I've got a bmw 435i RWD 8AT with full bolt-ons and a Quaife LSD.

Recently i've noticed the car has been acting up on cold start (mostly).

When starting the car there is a noticeable rattle from the rear (i believe exhaust or some component in the lower rear)

When I keep the car in D there is no sound, but as soon as I put it into N/R there are rattles/vibrations again, sounding louder in Reverse. (See Video)

When I drive away during cold start, 1st gear often requires 2500-3000 rpm to change to second, if I let go of the gas at higher rpm without the car changing into second the vibration can be heard like a "rRRrRRRrrR" sound.

Also (sometimes) when I start the engine warm or cold there is a small bang (think crackle/pop).

Have any had something like this before or know's where I should start looking? I dont notice anything different when driving, the car goes great in other terms.
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      03-09-2021, 04:40 PM   #2
thejeremyman9
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I've had the rattle from the exhaust flap before, and it didnt sound like your video. It also was not affected by gear selection.

Do you have stock exhaust? Can you go outside the car and listen around to pinpoint location?
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      03-09-2021, 05:48 PM   #3
Filip3615
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Quote:
Originally Posted by thejeremyman9 View Post
I've had the rattle from the exhaust flap before, and it didnt sound like your video. It also was not affected by gear selection.

Do you have stock exhaust? Can you go outside the car and listen around to pinpoint location?

I dont have stock exhaust, it's a Wagner tuning catless downpipe with a supersprint cat-back exhaust with an exhaust flap.

I can try and go outside the car tommorow if I notice the rattle. See if I can pinpoint the vibrations to a closer point.

I dont know what components could be making that sound from the rear. I wondered if it would be some issue with the LSD, but why does it go away in D and come back in N/R..?
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      03-10-2021, 12:28 AM   #4
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I just listened to the video again. It sounds like something loose and rattling against something else. It could just be the right frequency in N/R but not in D due to the way the drivetrain is loaded, just a thought. Since it happens in N though, i dont see how it could be something internal to the LSD. Did it happen right after that install? It's more likely something loose that could have happened during that install.
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      03-10-2021, 04:49 AM   #5
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Quote:
Originally Posted by thejeremyman9 View Post
I just listened to the video again. It sounds like something loose and rattling against something else. It could just be the right frequency in N/R but not in D due to the way the drivetrain is loaded, just a thought. Since it happens in N though, i dont see how it could be something internal to the LSD. Did it happen right after that install? It's more likely something loose that could have happened during that install.
Yeah that's been my thought as well, with the frequency.
The LSD is not new, it's been installed from the previous driver 2+ years ago.

But I think I will have to take a look underneath and see if I can spot some loose screw or such. Just a bit hard to pinpoint as it's not always rattling.

Do you have any tips where to start? Close to the exhaust flap or the screw's/ clams holding the exhaust parts together?
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      03-10-2021, 10:11 AM   #6
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that exhaust flap has this ghetto pin that connects it to the module...it tends to fall out causing an "unhinging" of the flap from the module and it makes an inconsistent rattling noise...i wonder if that's it. mine would rattle at idle but once i would start moving it would stop

Last edited by brigade24; 03-10-2021 at 10:13 AM.. Reason: claritin clarity
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      05-26-2021, 07:00 PM   #7
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I have a slight rattle from my ER catless pipe and stock exhaust. I think it's coming from around the area of the downpipe. I'm almost positive I didn't tighten the lower exhaust clamp enough but I have a question as to the function of this wire mesh in the pictures. What's the purpose of this wire mesh? It's pretty much loose at this point and I'm wondering if I should just cut it off and remove it. It doesn't really seem to affect how that area is joined.
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      05-26-2021, 07:28 PM   #8
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Quote:
Originally Posted by Polo08816 View Post
I have a slight rattle from my ER catless pipe and stock exhaust. I think it's coming from around the area of the downpipe. I'm almost positive I didn't tighten the lower exhaust clamp enough but I have a question as to the function of this wire mesh in the pictures. What's the purpose of this wire mesh? It's pretty much loose at this point and I'm wondering if I should just cut it off and remove it. It doesn't really seem to affect how that area is joined.
Yeah i dont know about your mesh, it shouldnt be like that i believe. However my issue was that the exhaust laid on the metall struts at the middle of The pipe and vibrated. No issue with the flap or exhaust really.
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