Hi, yes mine is exactly the same. The more load on the compressor- ie on a very hot day the more noticable the noise. Turning off the ac stops the noise instantly.
My previous mkiv
Ibiza was even worse, the noise was there from new although it never got any louder in the year I owned it.
To be honest I don't think this can easily be fixed, even changing the compressor is no guarantee. I think the
problem is due to the operating noise of the compressor being transmitted into the car via the air con pipes. Possibly due to the way they are routed and also a general lack of noise insulation.
Be interested if anyone does get it fixed though!