2.2 CDTI Tourer 2004.
A few weeks ago a strange noise appeared under the bonnet, on one occasion it sounded like a mechanical shaking, other times (more common) a nasty humming (think malfunctioning bearings), with more drive belt slip and squeaking than usual.
I removed the drive belt, started the car and the noise went away. Knowing it's likely in this area I fiddled with all of the pulleys and the tensioner pulley had far too much play in it.
I removed the tensioner pulley bearing and pressed in a new one, the strange noises are now mostly gone.
However, whilst this has helped, it appears to not be my only issue.
When driving now with climate control on, another "resistive humming" type noise occurs, it seems only to happen when trying to get the cabin up to temperature.
So here's my question, what could be happening, when asking for heat, to introduce a new load on the engine? When I'm driving and this noise is occurring, if I turn off CC the noise immediately goes.
I replaced the alternator a few years ago and did the shorter belt conversion at the same time.