Arfa Daily wrote:
Focus 1.8 Ghia Estate. 2000. Tad over 100k miles. Last night, it
suddenly started making a nasty noise from the engine, so bad that
even my daughter commented on it, and it's got to be noticeable for
her to hear anything wrong with a car engine ...

When it's idling, it sounds like a diesel. That's honestly the best
way I can describe it. As the revs build, it becomes more of a growl,
until at 2k, it smooths out like a switch has been thrown. I've had a
listen this morning with the bonnet up, and it sounds as though its
coming from around the front side of the engine, and doesn't sound as
though it's anything to do with the exahaust system. My tame mechanic
friend, who hasn't actually heard it yet, suggests a leaking injector
seat can cause this sort of problem, allowing excess fuel into a
cylinder at low revs, causing random detonations. This sounds a bit
fanciful to me. Anyone got similar experiences to share ? Anything
common on this engine ?
Thing is, it sounds worryingly like my little Fester did, when it
knocked an end out, and which ultimately led to my scrapping the car,
although that may have been slightly different in that the worst of
the noise was when you were on a light throttle at any revs, whereas
this definitely seems to go away as you pass 2k revs.

Any thoughts from the (far better qualified than me) 'usual
suspects', much appreciated.

d:-\

Arfa

try taking off the alternator belt and run it without to see if that effects
the noise.