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It's been doing this on and off since I got it. I've just replaced the mechanical fan with an electric one so the engine bay is hotter now and the screaming is happening more often. It does it when the fan belt is off so definitely not alternator or water pump. Noise appears to be coming from middle/top of engine.

Certainly attracts attention in town.

[youtube]http://www.youtube.com/watch?v=lLF0usZLSCA[/youtube]

A gas/vacuum leak of some sort I would say.

having now heard it -quite possibly head gasket/manifold gasket protesting

it could be the fibre pulley from inside the timing gear housing?

It sounds like a dry bearing, ball or roller. I agree to a degree on the gasket blow but it almost sounds at too high a frequency. Does it have a governor fitted?

Have you got a bit of hose and used that as a stethoscope to pinpoint the location yet? Also a long screw driver to do the same, pressed on the block or head and against your ear. Sorry if this is teaching grandmothers to suck eggs

when ditch described it to me my first thought was a bearing spinning in it casing cos mostly happening when the engine is unloading stress-decelerating-when load on bearing its ok.if it is bearing then most likely in timing chest or camshaft-but bearings 'normally' give a more consistent noise

Thanks lads. I'll wait till the sun is shining and start from the top and work down.

Can you pinpoint it to the front of the engine or not sure? I would have a guess at cam bearing - maybe excess float - shouldnt take too long to take front cover off ( although the pulley may be tight) and then you can also check condition of gears where there may also be a problem.

Noises always seem to bounce around in engines but I am pretty sure it's coming from the top of the engine and always seems louder on the exhaust side. I had the front cover off a while ago and the end float was fine then. Gears looked good.

Because of the electric fan I can now get it squealing reliably which makes tracking it down easier. Before I to drive it hard, slam the brakes on, get the bonnet up and get the listening stick in fast before it stopped.

You sorted this yet Ditch?

Still not sunny and the thing still runs fine. I'll pick my moment.

It may even just be a sypathetic harmonic vibration? they can be quite high pitched and quite baffling...until one day you move something that is acting as a 'tuning fork' and the noise goes away forever!!!! then you start to miss the noise and......well that's another story?