Renault V6 aircon noise

[rmunns]

My neighbour here (in France) has a Renault Laguna V6. He came to me for help the source of a noise that had just started. To me it sounded like a timing chain, if, that is, it has a chain and not a belt. But then Chris, the (english) neighbour, switched on the aircon and the noise got a lot worse. I didn't ask whether the aircon actually worked, but it seemed to me that whatever the problem was, it was likely aircon-related rather than timing chain/belt.
Maybe a stuck adjuster, which carries more load when the aircon is 'on'?
Could someone please help?

[xantia_v6]

My first guess is the compressor clutch or its freewheel bearing.

Or maybe a delaminating dual-mass crankshaft pulley.