Hi all,

My second post this week lol. long story short i have the transmission out of my car right now, and I'm trying to track down some gremlins. Since I bought the car it's made an odd scraping noise when decelerating or when I keep it at 3-4 k rpm in first gear. It's sounds like a sharpening wheel on metal, rotational and rhythmic but very grating. Almost like metal on metal brakes but not quite. Any thoughts on what it could be? It happens most audibly in first but also when engine braking on freeway, never tested to see if it goes away when brakes are depressed. I'm replacing my clutch and flywheel as well as my ground up cv axle, any chance either of those things could have been the issue? I've looked up the sound of bad differential bearings but it doesn't sound the same... I would appreciate any thoughts

 

Have you considered a bad wheel bearing? Those make quite the noise when bad.

 

I've thought about it, but usually that noise changes with speed, not differences in load right?

 

Well, wheel bearings would be a constant noise -- more like a dull roar in my case. Can I assume that you've checked the front brake pads aren't completely gone and making metal to metal contact with the rotors? That would cause intermittent noise especially when braking or decelerating.

 

A wheel bearing noise can change with a difference in load, much like differential input and output bearings, so that is a contender. Check to see if there is any play in the wheels when the car is in the air. Grab the tire by the at 3:00 and 9:00 positions, then again by 6:00 and 12:00 positions and try rocking it back and forth. Keep in mind, this isn't a definitive test and it can also highlight other suspension issues, but it's a good (free) place to start.

Another thing I'd like to suggest is wheel bolts, though you might have already removed your wheels given the work you mentioned. Make sure all of those are torqued up. I once left mine untorqued on my E36, and it was exactly as you described. Lots of noise on deceleration, none while accelerating or cruising at constant speed. Good luck!

 

Yep, checked brakes. I would try to rotate the axles but they're just hanging limp as the transmission is out, and the brakes are grabbing too much rn for me to move them by hand. I did find a rock in the brake shield that was causing it to be pressed loosely against the rotor, which could have been my issue. I also spun the carrier bearing on the RH axle and it sounded pretty crunchy, could be my issue. At first I feared that it was differential (might still be) but there are too many other variables that I'm not doing to crack the case and remove it. BTW, my noise sounds very similar to this... lmk if link doesn't work (go to 0:55). Once I get it all back together I'll be sure to torque down the lugs too

 

LR wheel bearing went out and symptoms were most audible 40-60 mph, below sounded like tire noise and above it disappeared behind the exhaust note. Didn't seem to depend too much on load although the car was loaded heavy (tools and spare parts weigh a lot!) at the time. No play in the wheel when shaking it though, didn't know for sure it was the LR vs the RR until I pulled it, and it was all kinds of nasty crunchy inside.

Might also go through the brakes and make sure caliper slide pins and brackets are properly torqued; outside-outside chance it could be that, given the pronounced note on deceleration but would think you would also have erratic braking performance, not sure...

 

Had a car get a twig caught between the rotor splash shield and rotor. What a racket. Managed to dislodge the twig by backing the car up and vigorously turning the steering wheel lock to lock.

Then same car -- some years later -- developed a horrible screeching noise as I was backing the car out of my parking space at work. Tried the trick that dislodged the twig. Not dice.

Had to jack up the car remove the wheel and pry the splash shield away from the rotor. A small less than pea sized pyramid rock fell out. Small rock. But oh my what horrible racket. Like gorilla fingernails on a blackboard.

 

Alrighty... so I've been chasing this noise for a minute now. Ended up pulling the trans and getting new pinion bearings/races, did wheel bearings on both sides, got a new cv axle, checked pretty much everything. I checked the trans over pretty good and it all looked fine, no extra play anywhere. Replaced the diff while I was there. Still the same noise! Could it be exhaust related somehow?