'Purring' vibration noise at idle and low revs

[fat controller]

My air filter housing has had the obligatory tie wrap fix applied on the first service, which seems to have solved that problem. In the past few weeks, however, a different noise has appeared. It is hard to describe, but it is a sort of 'purring' vibration, definitely linked to engine speed, which sounds as though it is coming from somewhere behind the speedo etc. It is present almost permanently at idle, and remains for a very short time when pulling away - when the revs get to about 1500, it disappears.

I reckon it is coming from the engine bay, with something vibrating against the bulkhead - but what? I do have self-adhesive foam (the sort that is used for HVAC installations for noise suppression) that I could apply if only I knew where to start looking -- any ideas?

[ragna]

Mine went into the dealers on thursday for what sounds like the same thing its not there when the engine is cold but after doing 10+ miles i get a faint vibrating/rattling noise which gets louder as the engine gets warmer you have to be in the car to hear it its not so audible outside,its difficult to tell just wear this noise is coming from but on revving the car above 1500 revs is seem to disappear at first i thought the noise was coming from the rear but now I'm not so sure. Dealer was not any help as they did acknowledge there was a noise from inside the car they said they were unable to find it as it wasn't loud enough and i would have to bring it back if it got louder.Hope you get a better response from your dealer than i did from mine.