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.. It's s driving me barmy only in 2 bedrooms upstairs. Is there anything you can do if it's just pipes expanding? (Have bled radiators, had system repressurised etc).
Sounds like water hammer. Check your radiator valves aren’t stuck (feel one side and then the other), top up your heating system, check for leaks (air in system), if it doesn't work consider getting an automatic bypass valve.
Could be pipes touching each other, can you get floors up to look. Could need a spacer. Or Could be air locked, bleed radiators in order can't remember of its first one closest to boiler or last one ask google. Remember boiler may need pressure topping up after.