[CCMDaytona]

OK, so since I bought it eighteen months ago my car, an E92 330i auto, has been running perfectly but two months or so ago, whilst I was pottering around town the engine began to screech/squeal. It only did it when I was driving on a light or trailing throttle or when it was idling. There was also a slightly lumpy idle at slightly lower revs. At greater throttle openings the noise disappeared. I parked the car and returned about an hour later. It started straightaway and ran perfectly with no roughness and no noise and it's been like that ever since, except that this weekend it did it again, exactly as before and in the same circumstances. I restarted it after an hour or so and the noise had disappeared and it's currently running with no problems.

Any ideas? I don't think it's the drive belts as the noise doesn't vary with engine speed but it does vary with the amount of throttle being used. And why does it come and go with long periods of faultless running in between?

[Phil325i]

I think you need to get the bonnet up next time it occurs and see if you can pinpoint the source. I recall a similar noise being reported from the oil filter housing when a non-OEM quality filter was fitted which was breaking up inside.