My 1985.5 944 has been making a metal on metal knocking sound coming from the rear left axle. Only when the car is moving. Tends to not be as bad when it is hot outside, but worse when it is cold and/or raining. Any ideas?

 

I would get the back end up on jack stands, with the stands holding the suspension as close as possible to the normal position with the weight on it, so I could run it in first gear and be next to the car listening. If that makes you nervous, get someone to drive you around while you are curled up in the trunk area to listen. Does it get worse under cornering, acceleration, or braking? Does it change when there is added weight in the back?

Of course, make a close inspection with the tire removed. Compare both sides, looking for differences.

Candidates are:
loose lug nuts
exhaust pipe hangers have failed
roll bar disconnected
shock broke or disconnected
constant velocity joints
wheel bearings
parking brake - with the wheel off the ground, engage the parking brake and see if it will hold the wheel from turning. It may be broken internally.
brake calipers
brake discs
bolts that hold the trailing arms in position have come loose

 

Weight in the back doesn't affect it, but acceleration does.

 

CV joints going bad possibility. Pretty common.

 

Lifted the car up this morning and let it idle in first gear to spin the wheels. Couldnt hear a noise, but I was pretty sure that it was the CV joints based on noise. So I degreased the joints on both sides and moved the half-shafts back and forth and that seemed to have fixed the problem for now. At least now if it starts to throw grease from a joint I can tell which one it is.

 

When they first start getting noisy you can take them off, clean all the old grease out repack with clean grease, then flip them. You’ll almost double the life of the axles doing just that.

 

I just did that same procedure after installing my KEP clutch.

 

+1 Yeah, definitely the CV joints. +1 As well on the rebuild. A little bit of a pain, but not a terrible job. Just tear them down where you have some space to lay everything out and repack them with a good grease, I used Mobil CMP on mine and haven't had an issues.