Whine from Mondial t/348 motor

Strange occurrance... in an '89 Mondial t - I have a strange whine sound (almost as a quiet version of an alternator belt slipping when wet squeal) from the engine. It only happens when the motor is at good running temperature, and I have given it some stick. Eg. if I'm on a clear road, going pedal to the metal up to 100 mph, then stopping at the next traffic light, then when it goes down to idle it starts with the whine... Not metallic or anything to suggest anythign scary. To add to the strangeness, if I switch the engine off, then immediately restart it, the whine goes away. If I drive along normally, it does not come back, but if I rip it on then it does come back. Everytime thoug, switching the engine off and back on seems to be the "reset"...

I did take the cam-belt covers off, and the belt looks OK - no bald patches, all looking normal. The belt service was done in Sept '06, and the car has driven 14K mi since (though 3K miles I did in 72 hours driving to Denmark, Paris and Milan all in one trip in a pan-European race with 2 Porsches and an Aston Martin - all youger than 4 years - and I won by being more disciplined, resting less and driving faster when the other's didn't dare - at night)

It really has me stumped. Not clutch related (same sound in-out, in neutral and in gear) - none of the accessory belts are slipping to my knowledge - alternator works tip-top (voltage & amp measurement), AC works fine, PAS works fine and exactly the same weather or not there is any whine.

Marco

 

There is a small leak which started a week ago when I replaced the thermostat. The whine has been there for a couple of months. Also, as I mentioned, it only happens if I give it stick (but not always), then goes away completely when I switch the engine off and on. Even if it is done immediately. Never happens if I'm doing calm city driving.