cling - clang.. what's that noise. BINGO *****

I found a new noise.
When I start off on a grade with a cold car I get a loud cling -clang tinny sound coming from the drive shaft or rear area (maybe). It is in time with the speed of the car and not the engine speed. When the car gets moving and is no longer asccelerating the sound decreases and stops or can no longer be heard. When driving the is a slight vibration when accelerating.
I check the universal joint by grabing the drive sfaft and trying to move and they appear solid. I tried to duplicate the sound by jacking the car and running the engine and turning the back wheels but no sound. Even tried pulling on the handbrake to increase resistance but no sound. The motor mounts are solid and the fan is not hitting anything.
When the car is completley warmed up, engine and drivetrain, the noise goes away. There is still a slight vibration when accelerating though. I might change the universals and see if that's it..
Do any of you guru have a clue ????
Hep..

Well, my mid goes right where yours did. U-joints, clutch or diff. The fact that it only happens uphill and cold sounds a little like clutch but "clang" doesn't. Find a grade where you can climb in 2nd gear at 3500rpm and shift to 3rd without accelerating. You'll find out if the clutch is slipping if the engine rpms go up and then down as the disk slips. Best of luck. Basil [PS, I wonder if the throwout bearing is sticking to the pressure plate and then making a clang as it gets thrown back???]

The u joint are still my choice but if doesn't explain why it goes away when warmed up. It would explain the vibration on acceleration. The throw out bearing sticking would be one cling not cling clang in time to the speed of the car.

Could the driveshaft or a U-joint be hitting the exhaust?

Bingo.... changed U joints and problem solved..... no cling clang no vibs... Just one greasy B boy...
The rear one as usual was shot. no lube in a permanemt lube joint. I should have changed them when I bought the car, at least I did buy them and have them on hand.

Thanks Basil for you help..