Not a good sound.
 

I swear lately this car is wanting to test my patience. However, I refuse to give up on the car. I've fixed so many things and it's been so much fun to drive. It performs well now, hesitation is gone, I fixed the exhaust, new O2 and she purrs like a kitten. This car finally runs like it should.

But I've developed a new issue.

A few days ago when leaving work I heard a strange rattling sound coming from behind me. I thought I was crazy so I turned my stereo down to listen, but it went away. I pulled up to the stop sign and pushed in the clutch. For a moment I heard a really strange whirring noise. The engine rpms had not changed, but there was an odd rattle/whir sound.

I pulled over, put the car in neutral, popped the engine lid and manipulated the throttle. I could not hear the sound, it was gone.

I got back in and the sound was still gone.

I drove home and about 2 blocks from my house at a stop I heard it again. Another rattle noise. I pulled over again, popped the engine lid to listen and manipulated the throttle. I absolutely could not hear it from the back of the car. I got in but I could hear it a little bit.

Oddly enough, I just got back from the exhaust shop and the sound hasn't at all presented itself to me until /after/ this was done. But I was there the entire time watching the car worked on and checked it out after they were done, nothing was changed, damaged, hurt, scratched. So I figure this must be an odd coincidence.

This morning again as I left from work I came to the same stop sign and hear the sound. This time, however, I brought the throttle up a little more and the sound became VERY evident to hear. 2500-3000rpms was this horrible metallic grinding noise (mind you I'm now stopped, clutch in, 1st gear). I put it in neutral and tried to see if the sound went away by letting out the clutch (suspecting perhaps a throwout bearing) and the sound changed a little bit, however, I could still hear it ever so slightly, not as bad albeit, but still hear it.

I'm starting to lean towards a throwout bearing that is making contact with the guide tube. However, the clutch feels fine, I feel no grit, I feel no bad response.

The sound appears to get better once the car warms up. However, I'm still very baffled. The car has started to make the sound a little bit and slowly has become worse until this morning it had me worried.

Bearings in alternator are failing; common problem, easy fix. Grab the fan with both hands and see if you can move it other than rotation. Look to see if it has made contact with the housing.

Corse, Chain tensioner failure?
Fifty50Plus

If it were chain tensioner failure I could expect to hear it at the front of the engine couldn't I? I will check it nevertheless as that is nothing to take lightly. Good suggestion. Would it also make the whirring noise? I've heard people describe that as "chain being dragged over a trash can" but this is pronounced yet not that violent. I will still check.

On the alternator bearing, that's a very interesting suggestion as I just had it replaced and its possible if one of the bearings is bad in the new alt (that was only weeks ago). I could try taking the belt off and spinning by hand I suppose. curious, could belt vibration cause premature bearing failure? I noticed recently the belt vibrates a bit yet looks solid around the pulley itself.

I think to alternator ball bearings , or fan.

This sounds a lot like a problem I had with an alternator a number of years ago, my VW rabbit. In diagnosing it, I took the belt off the alternator and ran the car for about 3 months without hearing the noise until I could afford a new alternator. If you conserve energy and only drive during the day, it is amazing how long you can go on battery alone. My record was 400 miles to Pittsburgh in my old mercedes.

What did you have it replaced with? Some of the readily available pieces from the local parts store are total junk. They a "rebuilt" with Chinese bearings that are bad upon installation. If it is a bad alternator, have yours rebuilt by a reputable local shop. I just had it done for $85 that included new front and rear bearings, brushes and diodes.

Also, who did the installation? It's quite different than installing on a regular car. The alternator needs to be seated squarely in the fan housing or the fan and pulley will not run true.

Rebuilt by a local shop. I installed it myself. I'm not sure which bearing they used but I'll find out tomorrow.

alt issue is one level of concern if you have tensioner issues that is a different (higher) level, if you don't have the tensioner upgrade, consider doing now, it is a PITA but not as much as lunching the engine

you might have mentioned you have the upgrade but if not...

Definitely agree. I checked tonight and put my hand on the tensioner area and feel no vibration. I feel some vibration from the fan if i put my hand on the top of the housing.

I do not have the tensioner upgrade.

I'll pull stuff apart and tear into it tomorrow. Definitely do not want to ruin the engine.

Possibly a worn chain, causing the sprocket to rattle until the tensioner reaches full pressure.

This might be more evident with cold oil, especially if the car was parked on an incline.

My car made a strange rattling noise under acceleration especially when cold. Ended up finding a few broken Dilaver head studs in my lower valve covers. Sure hope that's not your problem........ Good luck

You didn't tell us the year of the car. I'm assuming it's the 82 SC. I don't think that year had the dual mass flywheel but my 92 C2 made the same sounds when the flywheel failed. Throw out bearing failure can make noise even when the clutch is not depressed also one of the clutch spring elements can fail and make noise.