Sorry, i'd forgotten i'd replied to this post

To be honest i wouldn't know where to start. Problems like this i leave to my trusted locall mechanic. Sorry mate. The only reason I new it was the release bearing on mine was when said mechanic jumped in and test drove the car. He was confident it was the release bearing due to the types of noise it was making and the situations at which the noise would eminate.

Mine made a warbling sound when the clutch was engaged without a gear being slected (basically showing early signs of wear). It not a real noticable sound, you'll only hear it when you know what to listen for. I picked it up in my garage as it was amplified with the echo's.

The mechanic said that when they wear to a serious point they become really noisy and start to squeal and knock. Thats why I'm thinking it may be your release bearing. Only thing I can recommend is to get it checked by a professional.

Graham.H, kangarooing can be caused by a worn clutch/release bearing. Don't know the exact reason why, something to do with the spring plate not cushioning transmission vibrations or something. A faulty map sensor can also cause kangarooing as the car may experiance a slight miss-fire on overrun. This also happened to my previous sierra. Got it diagnosed on a rolling road.