A/C whirring sound

Switching on the A/C of my C3 Picasso (1.6 diesel ) produces an annoying whirring sound that changes when revving. It's similar to the sound made by the extractor fan of my gas boiler when a bearing is about to fail.

Searching online suggests it might be the aircon compressor itself, the pulley bearing or the clutch.

Has anyone here come across this problem?

Have you owned the car from new?

Have you had (or do you know if) the system has ever been re-gassed, at all?

There are 3 possibilities
1. The compressor is mechanically faulty. Typically...just worn out. Internal bushing or pistons.
2. Low system oil. If the system has had a leak at some time and has lost oil but not been topped up.
3.Low refrigerant. The oil AND refrigerant "dampen" the compressor noise. If the performance of the air condition system seems to be below par, it could be low on refrigerant.

Problems with the clutch tend to cause the compressor not to "kick in".
Problems with the clutch bearing cause a squealing or grinding noise.
If its a "clackety" noise, its the compressor (as above). Try a re-gas.

Thanks for your reply.

The car is a recent purchase from a Citroen dealer. No idea if it's ever been re-gassed. The sound is similar to that shown on a C3 here:
Closer to squealing/grinding than clackety.

The dealer has proved unresponsive so I'll just leave A/C off for now and ask my local mechanic to check it out at the next MOT.