Diagnosing a new rear-end "popping" noise

[eisen]

Hi guys! I'm having trouble tracking down this popping noise in the rear that started after my last track day. Does this sound familiar to anybody? https://www.youtube.com/watch?v=N8RqJM3vwbw Last clip was from closing my phone in the trunk.

Some notes:

• '02 with 160k miles (but lots of maintenance and suspension goodies)
• Rebuilt 4.10 M Variable Diff from diffsonline and poly bushings throughout subframe + diff. Everything has ~5k miles and 4 or 5 HPDEs.
• Rear subframe is reinforced with plates
• Happens most noticeably when accelerating from a stop, occasionally happens after rapid throttle/lifting. Slow circles clockwise or counterclockwise don't have a noticeable effect.
• No weird vibrations/noises otherwise.
• Haven't been able to recreate it on jackstands so far.
• No noise over bumps. RSMs look OK. I lubed the rear spring perches just to see if maybe the springs were sticking.
• No noticeable play in CVs, driveshaft seems to be OK.
• There's a bit of evidence of a leak at the diff input seal. It's tough to see but maybe that CV is slinging grease around there too? If it was a bad CV I was expecting more of a constant "click", though.
• I did have to retorque my front diff bolt a little while back to fix a "clunk". Other bushings appeared to be tight.

Thanks for any ideas! I'm not a great mechanic but I've tried to do my due diligence. My current plan is to do another nut and bolt check before moving on to replace the driveshaft CV joint and diff seal (as that needs to be done anyways).

UPDATE: A couple of the torx bolts from the axle to the diff were loose. Tightened them to spec and voila, no more noise.

[D-O]

Maybe this?

https://nam3forum.com/forums/forum/main-forum/e46-2001-2006/163489-clicking-from-driver-s-side-rear-wheel-area

D-O

[eisen]

Maybe this?

https://nam3forum.com/forums/forum/main-forum/e46-2001-2006/163489-clicking-from-driver-s-side-rear-wheel-area

D-O

Wow, thanks D-O! Not sure how I missed that thread while digging, but this seems totally possible -- symptoms seem to match at least. I probably just need to tear everything apart back there. The boots look fine but who knows how old everything is.

[sapote]

Rebuilt 4.10 M Variable Diff from diffsonline.

I think it’s the Diff clunk noise.
so add more flat shim on the side-gear (opposite of the pump side) to reduce spiders/side gear backlash.

[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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[bigjae46]

Guess here…I’d say it’s the axle. These cars are old, it’s worth at least cleaning and repacking the axle CV’s. I’d just go ahead and replace the boots.

inspect the ball bearings for flat spots while you are in there.

[eisen]

Thanks, all! I'm definitely leaning toward the axle. I'll report back once I have a chance to tear into everything.

[L0okitzRaj]

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)

[eisen]

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 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.

[PSUEng]

Check your diff bushings, at your mileage, I'm going to guess they are shot. They just disintegrate.

EDIT: re-read your post, maybe this isn't the issue, but I'd check anyway.

[sapote]

• Happens most noticeably when accelerating from a stop, occasionally happens after rapid throttle/lifting. Slow circles clockwise or counterclockwise don't have a noticeable effect.

From the symptom, I don't think bad CV joint as the noise should be there after rolling but continue acceleration.

Noise when acc from stop and during rapid throttle lifting is the sign of Diff clunk as the torque reverse direction previous moment (decelerate to stop then accelerate, and acc before lifting throttle).

[eisen]

From the symptom, I don't think bad CV joint as the noise should be there after rolling but continue acceleration.

Noise when acc from stop and during rapid throttle lifting is the sign of Diff clunk as the torque reverse direction previous moment (decelerate to stop then accelerate, and acc before lifting throttle).

Thanks sapote - that's what throws me off too. I know next to nothing about diff internals (much less how to add shims), but I'll do some more research. As it's a new noise, could it just be part of the diff "breaking in"?

[fattycharged]

Check your diff bushings, at your mileage, I'm going to guess they are shot. They just disintegrate.

EDIT: re-read your post, maybe this isn't the issue, but I'd check anyway.

on this note, I learned I have actually been running the e36 bushings for a loooong time now, easily 60k+ miles and didn't notice till I just dropped the diff. They look great btw, no cracking of the rubber, seem to have close to the same deflection as the new set I was planning on pressing in and trying them out....so FWIW I wouldn't hesitate to run them again and plan on it.

[fattycharged]

From the symptom, I don't think bad CV joint as the noise should be there after rolling but continue acceleration.

Noise when acc from stop and during rapid throttle lifting is the sign of Diff clunk as the torque reverse direction previous moment (decelerate to stop then accelerate, and acc before lifting throttle).

I'd have to lean towards this as well. I doubt I can recreate this exact sound with the diff on the ground, but mine has a lot of play and creates that "TINK" noise with the change in fwd/reverse load even when loading it by hand

[bigjae46]

I'd have to lean towards this as well. I doubt I can recreate this exact sound with the diff on the ground, but mine has a lot of play and creates that "TINK" noise with the change in fwd/reverse load even when loading it by hand

That is normal. The ring and pinion gear in the diff has lash or play.