Strange Noise Driving Me Potty

Hi all,

Was wondering if someone had any ideas of this random noise I keep getting.

It is coming from under the bonnet and the best way of describing it is like a belt rubbing.

However, it is not there all the time and only at very low revs when you are not accelerating, a slight touch of the throttle and its gone.

Has been checked at 2 independent garages neither could locate the fault.

Car is 2004 1.8T Petrol.

95,000. Full timing belt and water pump has been done.

Full auxiliary belt changed and tensioner changed. 

Fluids changed regularly.

Past its MOT and garage stated that the emissions where perfect, engine was displaying figures as if new car / new engine.

No smoke, turbo kicks in at 2,000 revs and gear changes are smooth.

Not sure if linked as haven't had car very long is that the pick up can be somewhat slow, like being pulled back unless you give it some aggressive throttle. Like I said, could be the car design as haven't had very long but thought was worth mentioning.

I mentioned to the garage if it was the PCV valve thingy bobby but they didn't seem convinced.

I think, that the noise if coming from somewhere behind the engine or maybe to the right hand side rear (as if the bumper was at your knees and you where looking at the front window).

Any pointers would be great, it runs like a dream great on fuel which really surprises me considering the road tax is fairly high.

Oh forgot it is a manual, I have dipped the clutch when the noise comes on thinking maybe thrust bearing / clutch related, this done nothing. Slight throttle tap and goes again for few minutes.