Have had an intermittant loud noise, drivers side under hood. Sort of like a bearing in the A.C., sounds like something unlubricated about to fail. Kind of a roaring once in a while.

Had the AC compressor replaced, cools great, noise re-occured.
When I run without AC, it never occurs, when I shut off compressor, it slowly goes away, not instantly.

Alternator being loaded up with AC ? I'm at my wits end!

What do the gurus suggest? 1983 300SD, 165K approx, R-12 system.