I have R registration fiat brava 1.4s has 50 thousand miles on clock, working fine apart from what sounds like a slipping fan belt noise. It seems to be coming from the top left hand side of the engine if looking under the bonnet from the front of the car. As if maybe even coming from under the rocker cover. The noise seems to only happen when i first switch on the car and especailly when i rev it a bit and then after a few minutes the noise seems to disappear completely. Does anyone have any ideas.

Alternator belt. Make sure there's no contamination on the belt and that it's in good nick and tighten it to Fiat specs. Easy job. If you've got other belts like power steering or air con then it could be them but if it's just for the first few miles on first start then odds on alternator belt is the culprit

i would fit a new cambelt at 50 thousand anyway, and do other belt at same time

well folks i finally managed to solve the noise problem, the noise in question sounded like a chirping sound. And it turned out to be one of the exhaust manifold bolts was loose.

cheers