Whining sound when hot

[arnebret]

Hi,

I recently noticed my 951 making a whining noise (like a belt not being properly set). I tested with p/s belt removed, no effect. Checked my distribution belts, no visual signs over there either. They feel good and they still look brand new (about 10kmiles on it). The other thing i noticed was that the sound only develops at revs above 3000rpm and only when the engine is warm. It's there in all gears, at all speeds, but i think it's especially there after a high-boost moment.

The strange thing is: the whining disappears when i depress the clutch -> rev drops back, sound disappears... With the clutch depressed (while driving) i tried to create the sound by revving the engine a bit, but nothing happens. Everything sounds fine. When i then but the clutch back on again the sound is still gone... But after a while it comes back.

Another strange sound i can't put into place, anybody out there that can?

Thanks!