Ok... Need some serious help - The other day i started my car up and could hear kinda like a squeeking belt from the engine, so opened the bonnet to hear nothing. Then to check i just revved the engine a bit from the engine bay, but when i let off the throttle i could hear a kind of vibrating/knocking this was in time with the engine (sounded a bit like if you have a sander turned on and touch it gently on a solid piece of wood) then when the revvs dropped a bit it stopped but did it again and again each time i revved it... after it had warmed up after a short drive to the mechanic - there was no sound at all but later when it had cooled i started it up and checked... and sure enough... there it is again. I'm not sure if it's the turbo buggered or something far worse! It's difficult to figure out where the noise is coming from. It kinda sounds like it's to the right of the engine but also sounds like it's down the back of it... Any ideas? Cheers!