Here's one which surprised us ...

Symptoms: After starting there's a very loud ratting sound (sound likes a chain slapping on the side of something), which then sounds more like gears grinding. Very loud, people stop on the street to look! Only happens on engine run down from about 2000 revs to idle. NO noise at all on revving up - smooth as a baby's botty. So, if you drive and change and don't go below 2000 revs, you don't hear anything.

The noise happens withe no gear selected, and the clutch in or out. and stationary.

AND ... after driving a couple of miles it stops making the noise altogether and the car performs well. Stop. and let it stand and we start all over again.

The noise (well its cause) has never affected the cars performance at all. The only indication of what it might be was the rear sensor tripping the engine management.

Well, to cut a long stroy short - it was the cat which had disintegrated inside - the exhaust gases were causing a vortex in the cat, and the bits of metal were rotating inside (hence the sound like a chain!).

Why did it stop after a few miles? One thought was moisture form the engine bound the bits together.

So, not all that rattles and grinds is gears or bearings ...

£330 pounds later - and all is fixed, new cat and manifold (all in one jobby!).

Rob