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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 Sat, Jan-20-2018, 09:07:10 PM   #1
///ALpineVert
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Default Help diagnose rear knocking noise

The sound can be heard at low speeds, not always there. I can’t hear it when the car is cold, I hear it after it’s been driven a bit. It is coming from the right rear.

ETA: CSB and guibo were replaced 1k miles ago.

Can you tell what it is?



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Last edited by ///ALpineVert; Sat, Jan-20-2018 at 09:39:36 PM.
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Old Sat, Jan-20-2018, 09:49:41 PM   #2
mrgizmo04
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Default Re: Help diagnose rear knocking noise

To me sounds like maybe loose diff bolts/bushing? Check bolt torque for front bolt especially. What condition are the diff bushings in?
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Old Sat, Jan-20-2018, 10:57:50 PM   #3
///ALpineVert
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Default Re: Help diagnose rear knocking noise

The rear diff bushing I can see looks ok.

I’ll check the diff bolt tomorrow when I get it off the ground.
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Old Sun, Jan-21-2018, 01:30:34 AM   #4
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Default Help diagnose rear knocking noise

You can easily get to the front diff bolt by lifting the rear right of the car and using a 7mm to pull the one screw holding onto the plastic shield to flex out of your way. Then a 21mm with short extension 1/4 drive torque wrench should be able to get in the front diff bolt. Youíll need it to be 148lbs of torque.

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Old Mon, Jan-22-2018, 12:02:49 AM   #5
///ALpineVert
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Default Re: Help diagnose rear knocking noise

So...I went to put the rear up on stands to troubleshoot and went to pre-loosen the wheel lugs. I discovered hat the rear passenger wheel lugs were loose already. So I’m relieved and terrified at the same time. Relieved that tightening the lugs fixed it, but terrified at the thought of what could have happened.

I check them before every autox, did last month. It’s almost like someone loosened them on purpose. Yikes.

Thank you for all of the ideas and help. Dodged a bullet on this one.
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Old Mon, Jan-22-2018, 12:28:23 AM   #6
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Default Re: Help diagnose rear knocking noise

Wow yeah. Thatís one thing I always take for granted. Itís happened once to me and all wheels were loose. I caught it within two blocks of the sound happening and retightened.
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Discussing Help diagnose rear knocking noise 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)