Help. Horrible Grinding sound.

[88SuperETABD]

Okay, so I was driving from home back to school on the freeway...maybe around 55mph I downshifted to 4th gear. As I did that, i hear a "grinding" like noise. It sounded like something was grinding my driveshaft. So I get to my dorm. And the next day i jack up my car. Checked underneath, my driveshaft has no marks on it and is not hitting anything.

This grinding noise only happens when the car is driving. In neutral, or in any gear. If i'm moving it happens. It also only happens when i'm decellerating (off the gas) If im accelerating, the noise doesnt come until i lay off the gas or even out.

Weird thing is, I jacked the rear of my car up. And put the car in gear and drove (with wheels spinning in air). The noise wasnt there...in any gear. Which was odd.

I dont know what to do...i know my tranny is leaking and has been leaking. What does my problem sound like to you guys? Sound like low tranny fluid?
Any info would be great. Feel free to ask me more questions.

[88SuperETABD]

No ideas guys?

[McGyver]

i think if you bring me your seats the sound will go away.

[brantleyr]

wheel bearings?

[10Toes]

Sounds like it's your transmission. I would get a good used transmission and swap it out.

[88SuperETABD]

could it just be that i'm low on fluid? Cuz its had a slow leak for a while.

[88SuperETABD]

wheel bearings?

Wheel bearings seem okay. Ive replaced one of the rears... all the wheels feel solid. It sounds like its coming from under the shifter. So...we were thiking transmission...maybe pressure plate? Or something.

[KennyT]

Sounds like a clutch actually. Does the noise change when driving and the clutch is disengaged? You could have broke a puck loose on a beat up disc. Don't drive it and pull the tranny as soon as you can.

[88SuperETABD]

I'm not driving it...but its stuck in a school parking garage. (Not in driveway). The clutch has no difference in the noise. It can be in or out...and the noise happens. Any time I'm moving it grinds. Its like the noise comes only when driveshaft is spinning

[Vtec?lol]

Sounds like your u-joint or csb is shot. Check the flex disk and then the csb. Try to turn the shaft by hand and see if you feel any kink spots.

if nothing, fill you tranny up and use lucas. check your motor and trans mounts.

[88SuperETABD]

motor mounts are 3-4 years old. tranny mounts looks okay. My csb (aka guibo right?) is brand new. no cracks no nothing. We are suspicious of the u-joint...that came up..but its just in a horrible spot(in a parking garage where i cant work on it)

[TS323]

maybe its the diff?

[88SuperETABD]

maybe its the diff?

doesnt sound like it...i just had that diff put in. Lower mileage than my car. everything was opened up...everything was clean. put redline in it.

[accident]

center support or guibo. and no, they arent the same. the guibo is a big rubber disc that goes between the drive shaft and the transmission output flange. it works as a bushing

[FLYNAVY]

I have the exact same problem right now with my M3. 4th gear only, accel or decel through about 45-55 mph. I don't think mine is as bad as the grinding you describe (it is just a little noise in mine), but similar symptoms otherwise. I have an s52 with a recently serviced good condition ZF trans, so perhaps it is something native to the e30 instead.