W126 Loud Squealing sound

[Mervyn]

Its unfortunate that this squealing problem came just about the same time as the difficult warm start problem.

The loud squealing sound goes "eeeEEEeeeEEEeeeEEEeee......."
alternating between a higher note squeal ("EEE") and a lower note squeal ("eee"). It comes on when the car moves on straight, and not when turning or reversing. And it only comes on after some driving, not when cold. I cant hear it on the highway, probably because the road noise is louder. But in the quiet carpark, the squeal is very much audible. No noise though when stationary with the engine running, so I've ruled out the belts.

Parking brake is off, springs and shocks are new, rims and tires are very new. I'm not looking for an exact answer to this problem as I know noises are hard to diagnose, but I would like to hear some similar experiences so that I could zero in on the source in the right direction.

Any clues anyone?

Thanks!

W126 1983 (280SEL)