When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I would have said it was a belt tensioner noise if you didnt mention its coming from the rear as the tensioner noise also lessens as the car warms...curious as to how it turns out...
you said it comes from the back of the motor.....are you sure? I had a noise that sounded the same and it drove me crazy attempting to figure out what was wrong.
It turned out it was just the belt. I did not believe it until after my guy changed it, the noise was gone.
My guess is dry pulley bearing - hard to find as some pulleys have inner and outer bearings - When I did mine recently I found 3 bearings showing signs of heat (Blued races) indicating lack of lube. most of my noise would go away at hot operating temps, drove me crazy for about 8 months.
JR