I was think bearings or something internal to the compressor. Sounds about right^

D3 should be permanently driven compressor without a clutch with a pressure regulating valve instead. Still could be making noise when putting load on it.

Dean had this with his S8 and it was the bearings in the compressor. We put a new one on and the noise was no more.

I actually had to label the compressor so I knew it was duff and didn't make its way in to 'good used stock', since you couldn't feel anything untoward spinning it by hand, and the clutch was fine. It was only under load at engine speed that it made the noise.

Just thought I'd add that before we went to France this summer I had the A/C's refrigerant replaced. The cabin was taking 15-20 mins to cool. I'd noticed over the years, it had been taking longer and longer to cool, but once cool kept cool.

The level of refrigerant was just over half of what it should've been.

Now the A/C is noticeably colder, quicker to cool and quieter. I'm not certain, but I think the fan isn't having to spin as fast etc.

Did 2,200 miles over the last few weeks in France and so far haven't noticed the annoying whine.

This could be because I had the wife and kids with me tho', maybe their whines were louder!

I'll have a proper listen tomorrow.