First off, I don't have much experience with cars. I've googled the issue and have come up empty.
I've got a 2006 Subaru Impreza Wagon with 170,000 miles. In the last month, a clunk has been occurring that appears to be coming from the rear of the car. It only happens when the A/C is engaged--and not all the time. I recently drove ~100 miles with the A/C on and I didn't hear a sound. At slower speeds (less than 50-55), the clunk is definitely there while the A/C is running--nothing while it's off. The mechanic thinks it's a bad wheel bearing and worsening rear differential. I don't doubt those are getting worse on the car, but what would the A/C have to do with these issues? What is the connection between the A/C and clunking. Does anyone have any ideas?
In January, the head gasket, clutch, timing belt were replaced. I added refrigerant for the A/C about two months ago. Regular oil changes.