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noticed a squealling noise from my focus couple of weeks ago, only there once warm and at idle speed (900rpm)
When I first heard the noise and had a quick listen to the area I assumed Alternator as in that area of the engine bay (driverside towards bulkhead) also seemed that it was when lights and blower on etc....
Anyway ordered new alternator and fitted it today, noticed the belt tensioner was worn so also replaced that (£72!!!!!!) and a new belt.
fitted back together...warms up and the idle drops to 900rpm and you guessed it squeal................ raise the revs slowly and its gone by 1100-1200rpm.
When I turn the engine off while squeal is there it continues almost as a pressure drop??? I'd say its slightly longer than the final engine rotations as the ignition is switched off.

Any ideas? has new alternator,belt and belt tensioner. noise is from the top side of the engine driverside towards bulkhead(near end of fuel rail)

its doesn't effect how the car drives or idles in anyway.

 

Hi! I think I have the same squeak as you describe in this thread, have you found a solution? I'm thinking it could be the rear engine/gearbox bushing mount, but I don't really know.