Diagnosing a new rear-end "popping" noise

[fattycharged]

Yes, but only to an extent…I've currently two in front of me to compare and one is not like the other


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[fattycharged]

Double post

[VinceSE2]

It's very hard to tell from a video clip, but to me it sounds like sheet metal panels creaking against each other and popping from one side to another as the load shifts.


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This has also been floating around in the back of my mind and scares me.... The plates were done a long time ago and the bushings done by a shop the previous owner used so I can't be sure how thorough they were. I should probably do an inspection just in case.

Also a guess here, but I assume the subframe was inspected on last bushing replacement? ...but possiblly racp has cracked and it's metal moving around/rubbing on the tear (i know you said plates were installed)

This is what I was hinting at in my previous post.
My guess would be the panel separation in the left wheel well due to popped spot welds.

Please have a look at these videos for some insight on the underlying issue, where to look for damage, and how the VinceBar kit addresses said design issue:

https://youtube.com/playlist?list=PLg2TArrteKd4ttsu_Nr1SznnEw9N81cN7

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[eisen]

This is what I was hinting at in my previous post.
My guess would be the panel separation in the left wheel well due to popped spot welds.

Please have a look at these videos for some insight on the underlying issue, where to look for damage, and how the VinceBar kit addresses said design issue:

https://youtube.com/playlist?list=PLg2TArrteKd4ttsu_Nr1SznnEw9N81cN7

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Thanks, Vince - I appreciate it! I'll queue up the videos tonight and hopefully have some time to give the car a thorough check this weekend. I'll report back with what I find.

[eisen]

This is what I was hinting at in my previous post.
My guess would be the panel separation in the left wheel well due to popped spot welds.

Please have a look at these videos for some insight on the underlying issue, where to look for damage, and how the VinceBar kit addresses said design issue:

https://youtube.com/playlist?list=PLg2TArrteKd4ttsu_Nr1SznnEw9N81cN7

Sent from my iPhone using Tapatalk

Well, I couldn't resist taking a quick look since the car was already on jackstands. A little simple green and.... yikes 😬

[Mayan-Viking]

Damn, That sux. Damn, great call Vince.

[eisen]

Seriously, Vince - can’t believe you pinpointed it just from a short video and some symptoms. Clearly you’ve seen one or two of these! Haha.

Appreciate everybody for chiming in. I’ll have to evaluate my next steps - was planning to put a half cage in at some point so this might be the time to knock everything out.

[Mayan-Viking]

Seriously,
Appreciate everybody for chiming in. I’ll have to evaluate my next steps - was planning to put a half cage in at some point so this might be the time to knock everything out.

Exactly. This is the impetus you needed to bring it to the next level. Pretty much out of your hands at this point. Great looking car. It will only get better when done. Good luck!

[eisen]

Exactly. This is the impetus you needed to bring it to the next level. Pretty much out of your hands at this point. Great looking car. It will only get better when done. Good luck!

Now that's the positivity I need right about now -- cheers!

[Thoglan]

Now I'm worried, I'm pretty sure I've heard a similar noise from the rear end of mine (slight clink or pop under acceleration) and I've had topside and underside reinforcement, already had my wheel arch seams welded once... I had assumed it was an RTAB, guess I'll have to go have a look now :P

[sapote]

Well, I couldn't resist taking a quick look since the car was already on jackstands. A little simple green and.... yikes

The cracks or floor seams separation in the photos are still in the early stage, and so I wonder if the squeaking noise could be from other areas that have longer cracks to cause the panels flexing more. I'm interested of what you will find more when the diff/subframe are removed
Listening the video a few more times and it became more clear now that this is a multiple squeaking noise as opposed to a single clunk of the Diff when the torque changed direction.

[eisen]

Well guys, I found the source of the noise, and it wasn't the RACP (hallelujah).

TLDR: A couple of the E torx bolts that secure the axle to the diff were loose.

I spent most of the day digging through the rear of the car looking for signs of any other cracks. Everything looked fine; I even scraped up some of the sound deadening in the trunk and couldn't find anything that could be causing a noise like that (thanks for making that point about it being in the early stages, sapote , it made me want to look for other evidence).

Finally decided to go back through and retrace my troubleshooting steps just in case. After messing around with the driver's side axle, I remembered reading online about those torx bolts from the axle to the diff coming loose on racecars. Decided to check mine just in case and, what do ya know, a couple were loose - one fingertight. Still wasn't convinced that could do it, but torqued them to spec, noticed that it got rid of a tiny bit of play that was there, lowered the car down, and voila - no more noise. What a rollercoaster. I'm planning to order some new ones, loctite them, and hopefully never deal with this again.

I'm still in need of topside reinforcement and to stitch weld that crack in the wheelwell, but at least it isn't urgent.

[bigjae46]

That’s good that you found the issue. I’m always paranoid that I missed a bolt so I usually double check them.

I have a new set of axle bolts if you need them. Send me a PM if you’re interested.

[sapote]

TLDR: A couple of the E torx bolts that secure the axle to the diff were loose.
.

Great. A completely loose half shaft at high speed will swing around, hit and damage things around. As the diff was removed before, so the bolts backing out were not torqued to the factory spec is my guess.

[bmwfnatic]

I'm still in need of topside reinforcement and to stitch weld that crack in the wheelwell, but at least it isn't urgent.

From personal experience, I also have a previously plated car that was en-route to fail again.

You have basically popped all spot welds that kind of ‘let go’ peacefully, the 3 along the wheel arch and at least one visible near the left spring perch (usually at least one more but hidden by thick seam sealer).

Your entire rear left rear mount is pulling away from the car and not held in by much anymore, the next stage is for the panel to start cracking (as mine did), so to prevent further damage (which is much more difficult to repair compared to the stage it is in now, I would say it is somewhat urgent.

In addition to this damage at the rear, the front of the RACP was also pulling away on my car, with all 8 of the spot welds (4 per side) where the RACP attaches to the rear seat area having let go.

I am not trying to scare anyone but in my opinion based on my findings repairing my own M3, the topside reinforcement is very important.