Strange Shrill Sound Under Bonnet

[My Car]

I have a strange high pitched shrill sound under the bonnet,that increases and decreases with engine revs. but only lasts for about 10 mins. then stops,Could it be a bearing somewhere in there and if so how do I test to find out where it could be.Thanks for your help poeple. Martin

[Panama]

check your belt tensions.

belts may only squeal when cold, or under sudden load, ie revving.

you may have a glazed belt which would be indicated by a shiny contact surface.

better off replacing any belts that are glazed.

[Jase_81]

Could be manifold exhaust leak that goes away when engine warms up.

[Goon]

Make sure ur not getting any oil on the belt from leaks..

[harry3]

my first thought is loose belts

[jatsvl]

get a bottle of water and pour it on the belts while the noise is there if the noise goes away its the belts!
loose, glazed or oily.

[My Car]

Thanks guys for replying, turned out to be slack belt,ajustment to idle pulley,fixed,easiest job yet.The water tip, great idea.Thanks again all.
Martin