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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Wed, Sep-19-2018, 05:41:04 AM   #1
Boostadikt
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Default Rear knocking noise (don't fry me)

Preface: I know there are a thousand of these threads and I have tried searching, I've tried a lot of things, please don't hate me.

I have a nasty knocking noise coming from the rear end, it sounds like a rattle almost or something very loose. But here's the thing it only does it when I go over small bumps, and it is very pronounced. If I go over a big bump: nothing, it sounds very solid. Under heavy acceleration/deceleration also very solid.

I really have searched and tried *almost* everything as I will continue to investigate, but I just bought the car. I've had it on a lift a few times. I have looked over the subframe mounts 10 times and haven't found any cracks or anything that looks bad. I removed all of the trunk lining and again everything in there looks perfect. Everyone talks about RTAB, so I bought Powerflex bushings and replaced them a few days ago. The stock ones were actually in really good shape, but now with the new ones, same problem. I put the car on jack stands and shook the rear wheels with all my might and all of the bushings/ball joints/control arms look to be in great shape. The car has 106k miles on it. Everything to me looks great, but still the knocking continues.

However, when the car is sitting normally, if you bounce the rear end up and down you can hear it. It's just near impossible to pinpoint where the sound is coming from when you're bouncing on the rear end.

I'm getting exhausted of searching for this. What I'm hoping for is one of you to give me some more direction. Some bit of knowledge you have that will point me towards what I should check next. Anything you know of that is another common failure point? The car has Ground control suspension and everything on that is also tight. Anyways thanks in advance for the help!
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Old Wed, Sep-19-2018, 06:11:17 AM   #2
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Default Re: Rear knocking noise (don't fry me)

I have a similar noise driving around town, and I also have Ground Control suspension. I think it has to do with the spring mounts. If I remember right, it wasn't making that noise when I had the car lower, so maybe check how the spring interacts with the rear adjuster.
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Old Wed, Sep-19-2018, 07:21:09 PM   #3
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Default Re: Rear knocking noise (don't fry me)

On my stock suspension, two things that caused a clunk/noise - rear shock mounts & lower ball joints. Both very inexpensive.

When the shock mounts failed the clunk was felt throughout the entire car and I couldn't tell if it was front or back. That was one of the best ~$20 fixes ever lol
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Old Wed, Sep-19-2018, 09:01:12 PM   #4
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Default Re: Rear knocking noise (don't fry me)

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Originally Posted by Kdubski View Post
On my stock suspension, two things that caused a clunk/noise - rear shock mounts & lower ball joints. Both very inexpensive.

When the shock mounts failed the clunk was felt throughout the entire car and I couldn't tell if it was front or back. That was one of the best ~$20 fixes ever lol
That rsm knock sounds just like my knock but the rsms are new. How tight did you make that nut on top?
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Old Thu, Sep-20-2018, 02:42:45 AM   #5
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Default Re: Rear knocking noise (don't fry me)

Thanks, I'll check the shocks and ball joints tomorrow. I thought it could be the springs but it just seems odd if they would make noise over small bumps when basically still fully loaded.
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Old Thu, Sep-20-2018, 02:56:23 AM   #6
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Default Re: Rear knocking noise (don't fry me)

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Originally Posted by Boostadikt View Post
Thanks, I'll check the shocks and ball joints tomorrow. I thought it could be the springs but it just seems odd if they would make noise over small bumps when basically still fully loaded.
You mentioned you're on coilovers. As soon as I did subframe reinforcement with powerflex solid bushings & ecs camber arms - both lower ball joints failed within ~700 miles. It clunked on poorly paved streets but not cruising.



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Old Thu, Sep-20-2018, 02:57:20 AM   #7
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Default Re: Rear knocking noise (don't fry me)

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Originally Posted by icecream View Post
That rsm knock sounds just like my knock but the rsms are new. How tight did you make that nut on top?
As tight as it was on there before, dont remember. Could also be FCAB if they're bad

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Old Thu, Sep-20-2018, 03:29:52 AM   #8
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Default Re: Rear knocking noise (don't fry me)

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Originally Posted by Kdubski View Post
As tight as it was on there before, dont remember. Could also be FCAB if they're bad

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Everybushing or ballpoint or controll arm is new except sway bar bishings amd I still get the knock. Mainly mentioning that for the OP so they dont go down a rabbit hole like I did and still have the problem. I'm thinkong maybe its a panel or center muffler support, should have started with that.
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Old Thu, Sep-20-2018, 04:26:57 AM   #9
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Default Re: Rear knocking noise (don't fry me)

Have the same problem with Ground Controls, I've just been ignoring it for 3 years. The car has had them for at least 50k miles.
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Old Thu, Sep-20-2018, 04:47:58 AM   #10
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Default Re: Rear knocking noise (don't fry me)

i had similar problem

if the car has ground control weight jacks and 2.5" rear springs, the 2.25 to 2.5 adapter deteriorates over time. this causes the spring to bang about on the perch.
mine were flogged (only 1yr old), so i p!ssed them off and replaced with a machined aluminium adapter. no more noise
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Discussing Rear knocking noise (don't fry me) in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)