C3 noisy at idle

[pogo001]

Hi guys.
Hope you are all well in these strange times.
I’ve been struggling with a very annoying problem on my daughters c3 1.4 hdi 2005.
At idle it sounds like a bag of nails, and the aux belt tensioner is jumping around. I have replaced the main crank pulley, the alternator isn’t a clutch type pulley and runs smoothly. The tensioner runs smoothly. Today I changed the last remaining pulley, the three part air con magnetic clutch. I really thought this would solve the problem but no.
I have run the engine with the aux belt removed and it’s quiet and smooth at idle.
Any ideas???