My 91 940T has an annoying idle noise.For me to describe this,it is going to be difficult.It is a schee,schee oscillating sound.I am guessing that it must be a problem with a flywheel.All the belts are fine.This is a vague question,but its worth a try to see if anybody has had this headache.Thanks.

Probably V-belts. The pullies and belts become glazed and can make a screee, screee, screee sound. Or sometime it's cheee, cheee, cheee...

On my cars, it's a cheeeep, cheeeep, cheeeep sound...
--
Don Foster (near Cape Cod, MA)

Really hard to tell.
Although you say your belts are fine, spray them with water one at a time and see if it makes a difference just to rule them out.
Or it could be the timing belt tensioner, remove rubber plug in timing belt cover an listen with a stethoscope.
If it is really coming from the flywheel area it might be the pilot bearing in the end of the crankshaft. Requires tranny removal to change.
If it is a manual you also have the trow out bearing in the clutch, but this would only make a noise with the clutch depressed.

HTH
Mikael Larsson

Of course there are bearings in the alternator, water pump and AC compressor but those could be identified with a mechanics stethoscope/ long screwdriver..

Mikael Larsson