I recently had two new radiators installed and at first everything was fine. Now, two radiators (one of which was one of the new ones) makes a high pitch whining noise (although not all the time). I have bleed the radiators but they were all fine. The new radiator that whines has a thermostatic valve but the other radiator that whines is a lot older and does not. The two radiators are in adjacent rooms upstairs.
It is possible after fitting the new radiators, the system has been overbalanced by screwing down the lockshield valves too far. Try reducing the water pressure (and consequentially the noise) by opening up the lockshield valves on the offending radiators by about 1/4 - 1/2 turn.
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