A/C Question regarding noise
 

The original owner of the car didn't take any care of the A/C system. When I got it the car a couple years ago, the compressor was almost completely seized. I disassembled the system. I flushed the evaporator and the condenser and blew them out with high pressure air. I used high pressure air to clear out the lines.

I then replaced the expansion valve, compressor, receiver dryer, cabin filter, and all the o-rings on the entire system. I have my own air vacuum and manifold set, so I checked the integrity of the system which was air tight and charged the system myself to spec.

Here's my problem. I noticed that there's almost what sounds like a rattle noise coming from the compressor or near that area. You can only hear it with the A/C on, when the clutch engages. I thought perhaps the tension pulley might have been shot, so I replaced the tension pulley and the hydraulic tensioner but to no luck the sound is still there.

I finally tucked my tail between my legs and took the car into a shop with a really nice A/C service machine. The guy has done lots of misc work on my car and bike. He ended up not charging me because he said the poundage was exactly where it should be.

I'm totally open to suggestions.

Note:

Vehicle is 5-speed 96 328i with 175,000 miles.