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      02-15-2016, 07:45 PM   #1
Hrosen
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Angry Knocking noise from rear (help!)

Hi all,

Just bought a really nice 2006 3.0si coupe with 52K miles. Car seems very strong generally but when going over bumps/dips in the road i hear a distinct knocking noise (almost like metal clanking against metal) coming from what sounds like the passenger-side rear. I had a PPI done by my mechanic and they told me the suspension seems fine, but I don't trust them...

It literally sounds as if there's a piece loose/untightened. Any thoughts? Strut bracing, tie rods, what? I'm hoping it's not too pricey...

Thanks in advance!
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      02-15-2016, 09:46 PM   #2
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Inside the car or from underneath? My first guess would be the rear shock mounts or sway bar end links. Lay on the ground and have a buddy push down on the rear fenders to bounce the car, you might be able to distinguish where exactly the noise is coming from.

EDIT: I just noticed you said metal on metal, I'm not sure if it's a problem with the non-m's but the rear springs would occasionally break off one coil on the Z4M's and I believe it can cause that sort of sound as the piece either rattles around or the coil can unseat/twist when going over larger bumps
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      02-15-2016, 10:08 PM   #3
Hrosen
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It sounds like it's coming from inside the car... essentially from the right rear wheel well basically. It's like 10 degrees Fahrenheit here so I'm probably not going to be laying on the ground anytime soon next to the car But this gives me some sense of what it could be. I was just worried it might be an axle or something more involved which concerned me.

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      02-15-2016, 10:39 PM   #4
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Don't take a diagnosis from a random dude on the internet as gospel regarding a sound you can only describe with words :P

If you can't verify it, it's best to check it out however you can. Pop the hatch and do the bounce test yourself. If it's inside the car it should be pretty easy to single it out, I believe RSM's are an item that are good to replace early in their failure state cause I'd imagine that a catastrophic failure of one would let the shock potentially punch right up and inside the car (someone could correct this if it's not true)
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      02-17-2016, 06:18 AM   #5
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I just had the identical problem resolved on '16 Z4. The problem was indeed a shock mount.
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      02-17-2016, 07:47 AM   #6
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The first thing you should do is to check the bumpstops for the trunk lid.
Open the trunk and you can see two black plastic knobs, one on each side. When you turn on them they go up or down. If to low the lid rattles.
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      02-20-2016, 03:06 PM   #7
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I would check firewall braces, those tend to get loose. If noise is coming from rear could be rear shock mounts. I found in general the OEM bushings (fcab, rtab, etc) need to be replaced every 40-50k or so.
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      02-25-2016, 06:05 PM   #8
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Problem solved and a comment

Thanks for all your thoughts. I was happy to find out that it was in fact a loose bolt on a heat shield or something of that nature that apparently runs the length of the car. Having torqued that back up the sound is now miraculously gone.

There is still a creaking sound that I get from the rear (seems like it's coming from the plastic in the hatch). I tried turning the rubber hatch stops but that didn't do anything. Pushing on the plastic recreates the sound so I'm pretty sure that's what it is. Any thoughts on correcting the issue welcome.
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      02-25-2016, 08:07 PM   #9
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I have a creaking in the rear of my car when I park and get out of the car. Can recreate it by pushing down on rear fenders.

It only happened when the parking brake was engaged. I finally diagnosed it as the rear brake mechanism in the rear rotor that makes the noise. Drove me crazy until I figured out the cause. Will address it if I need to do when I do the brakes in 50K km or do.

Had creaking in the interior cab when driving.... That was the seat rubbing on the back of the interior cabin bulkhead.
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      02-26-2016, 03:47 AM   #10
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Quote:
Originally Posted by Clearancediver View Post
Had creaking in the interior cab when driving.... That was the seat rubbing on the back of the interior cabin bulkhead.
We lose a lot of leg room due to the speaker panel behind the seats.
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