Weird noise/vibration in cabin at high speeds - *SOLVED*

[Arith2]

This could be a compound problem. The wheel may have excessive roadforce and your diff could be on it's way out.
If you want to chase the diff:
For testing purposes, buy the LM stuff and add half of a tube. It doesn't really matter what brand. You can even get some GM friction modifier. Getting OE fluid is not cheap, however the tube is like $15. Mix it up a bit from some circular driving and go on a short drive. I doubt it's going to solve your problem considering you are driving in a straight line while the groaning is happening. Getting OE fluid is $150 and I can almost guarantee you it will not fix it. Diff bearings could also be failing. When you pop the fill plug off, stick a magnet down in there and see how much metal sticks to it. I hate to be the bearer of bad news but you may have something failing in your diff.

One last thing to consider is worn suspension under the downforce. Check for any scraping or leaking struts. This is a simple check and is highly unlikely but I have seen struts fail at 5k miles causing an oscillation at higher speeds. This would explain the changing of load and body roll. I'm still thinking you have bad tires and a bad diff though. I am not a fan of throwing parts at cars. That's not a diagnosis, that's a waste of your money.

[jayjpl]

This could be a compound problem. The wheel may have excessive roadforce and your diff could be on it's way out.
If you want to chase the diff:
For testing purposes, buy the LM stuff and add half of a tube. It doesn't really matter what brand. You can even get some GM friction modifier. Getting OE fluid is not cheap, however the tube is like $15. Mix it up a bit from some circular driving and go on a short drive. I doubt it's going to solve your problem considering you are driving in a straight line while the groaning is happening. Getting OE fluid is $150 and I can almost guarantee you it will not fix it. Diff bearings could also be failing. When you pop the fill plug off, stick a magnet down in there and see how much metal sticks to it. I hate to be the bearer of bad news but you may have something failing in your diff.

One last thing to consider is worn suspension under the downforce. Check for any scraping or leaking struts. This is a simple check and is highly unlikely but I have seen struts fail at 5k miles causing an oscillation at higher speeds. This would explain the changing of load and body roll. I'm still thinking you have bad tires and a bad diff though. I am not a fan of throwing parts at cars. That's not a diagnosis, that's a waste of your money.

Ah you might be completely correct with it being a compound problem. The PO from mine did not at all take care of this car (which is unfortunate and fortunate for me). I used to think my wheels were rubbing everytime i got onto the throttle from a low speed, but now i realize its actually the diff causing the thud.

Do you mean unbalanced tires? I've gotten those rebalanced and nothing. I agree with throwing parts, but nobody has been able to give me a straight answer. I managed to find a used diff, so hopefully that solves everything.

[Arith2]

Ah you might be completely correct with it being a compound problem. The PO from mine did not at all take care of this car (which is unfortunate and fortunate for me). I used to think my wheels were rubbing everytime i got onto the throttle from a low speed, but now i realize its actually the diff causing the thud.

Do you mean unbalanced tires? I've gotten those rebalanced and nothing. I agree with throwing parts, but nobody has been able to give me a straight answer. I managed to find a used diff, so hopefully that solves everything.

Most people do not know how to road force balance tires. Just because a shop says they use the feature doesn't mean they use it or use it properly. It could be a dented rim or just trash tires. I just returned a brand new continental because it road force balance at 60 pounds. Basically you want under 20 pounds. 20-30 is acceptable on our rims but anything above that you're going to feel. How are the control arm bushings?

Tackling the most concerning to the least is the way to do it. I'd say that diff is priority.

[jayjpl]

Most people do not know how to road force balance tires. Just because a shop says they use the feature doesn't mean they use it or use it properly. It could be a dented rim or just trash tires. I just returned a brand new continental because it road force balance at 60 pounds. Basically you want under 20 pounds. 20-30 is acceptable on our rims but anything above that you're going to feel. How are the control arm bushings?

Tackling the most concerning to the least is the way to do it. I'd say that diff is priority.

Control arm bushings are still good... thankfully. Replaced my diff with a nice used one, and groaning and shuddering at low speed is gone! acceleration is nice and smooth, not as much clunking in the rear anymore for sure.

*however* my initial problem is not solved. I'm leaning towards driveshaft, or driveshaft CV joint - a shop that inspected it let me know that it was on its way out. Could a bad driveshaft cv joint cause these issues?

[jayjpl]

UPDATE:

I'm absolutely 100000% at my wits end. I've replaced the driveshaft, CSB, and the Driveshaft CV joint, and its still there.

I honestly don't know what to do at this point and I'm debating on calling it a day, taking insurance off the thing and parking it till I'm mentally ready to tackle this.

[Stack]

I would change tires , but before that try to re balance them

Similar thing thing happened to my buddy
Brand new PSS

Sent them back to Tire Rack and received new ones

We had them balanced at a Race shop
No road force just normal balancing

Problem was gone


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[jayjpl]

I would change tires , but before that try to re balance them

Similar thing thing happened to my buddy
Brand new PSS

Sent them back to Tire Rack and received new ones

We had them balanced at a Race shop
No road force just normal balancing

Problem was gone


Sent from my iPhone using Tapatalk

was his problem a full vibration/shaking throughout the entire cabin? mine can be felt and heard in all corners of the car. It sounds like its in the rear but vibrates and can be felt, hence why others thought it was diff and driveshaft

[jayjpl]

Found a reverse torx screw is missing in my driveshaft where it connects through the CV and into the Differential. Will be installing that later this week, I've read that it can improve rear end clunk.

[jayjpl]

Hi all,

Issue has been solved! see the first post in the thread as there has been an edit as of June 14th, 2021.

[bigjae46]

Sorry I didn't see this sooner...I would have told you its the driveshaft CV. If its a high speed vibration....its the CV joint.

[sapote]

had a driveshaft bolt put in as one fell out.

Sure enough, my issues are solved. I am both ecstatic and livid, but now breathing a sigh of relief.

any chances that you removed these bolts and somehow didn't torque them to spec during installed the manual tranny?

[jayjpl]

any chances that you removed these bolts and somehow didn't torque them to spec during installed the manual tranny?

Unfortunately no… it happened before i did the manual swap, so most likely fell out at a random occurrence

[bigjae46]

Unfortunately no… it happened before i did the manual swap, so most likely fell out at a random occurrence

It fell out because it wasn’t properly torqued. Easy to do.


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[sapote]

Unfortunately no… it happened before i did the manual swap, so most likely fell out at a random occurrence

OK, but during the tranny swap, did you disconnect the drive shaft to the diff end?