Citroen Xsara noise

my car has a very strange noise under the bonnet ,its like a turning squeal,or squeak but not all the time ,ive had new water pump new belt tensioner,other pulleys r ok ,brakes ok all cleaned,wheel bearings no noise,no movement in driveshafts or bushes or rubbers ,no noise when still or revving engine ,noise only when moving,not all the time though,wondering about engine mounts but noise sounds like a spinning sound as though something is turning against something else then sticking then clearing please any suggestions appreciated