[xain]

I had an Astra that did the reverse of this. It was quiet when cold, then made a *real* nasty racket when hot. Turned out that the water pump was almost falling out because the bearings were so knackered. Maybe it's a similar problem, but the metalurgy might mean that it gets tighter with heat? I would try checking the alternator bearings. Can you get the belt off easily?

[dan]

Its not an air pocket in the oil pump is it?? I've no idea what this would sound like, but after having a recent panic attack following a zero reading oil pressure gauge I did a little reading up. Apparently its easy to get air pockets if you drain the oil or even if you are low on oil and corner hard (do you park on a slope??). If it is an air pocket it should be pretty straight forward for your mechanic to sort. Whatever it is I would get it looked at, as generally its better to get these things sorted sooner rather than later. Best of luck, and let us know how you get on. Cheers Dan