FredR

A/c compressors by nature of their construction tend to be a bit noisy but generally speaking I suspect we are not aware of them on the 928 because of where they are packaged. My a/c system has been working really well of late after I topped it up and I did not add any oil as I reasoned that previous top ups had probably added too much.

Recently I felt the motor was running a bit rougher than usual so took a listen in the engine bay with my stethoscope. After eliminating most of the kit in the engine bay I was left suspicious of the a/c compressor from where a bit of mechanical noise was emanating- switched off the a/c the noise I was hearing disappeared. Now the question is whether such noise that I was hearing is normal or abnormal?

I remember on my Subaru Legacy it made quite some noise and was a similar Denso type of compressor. On the Legacy it was mounted high up at the front and the noise bounced around the engine bay more noticeably. I complained about this when it was new and was told "they all do this". After the warranty period was over they proposed to change it- I then told the Subaru agents to "sod off". It stayed that way for another 10 years, still froze my nuts off and I learned to live with it.

Any comments or suggestions?

Majestic Moose

I have a fresh rebuilt compressor and it does not emit any discernable noises, at least nothing to be heard above the engine and cooling fans. If the bearings are nearing end of life, I wonder if the belt could be removed and then turning the pulley by hand, you could feel for any play or roughness.
If it were me I would leave it alone but have a rebuilt unit on standby given your climate. That said, I would be concerned about a failure cycling debris throughout the AC system.