There's a hot water wall-hung radiator in my kitchen that produces a constant ticking noise when water is flowing. The noise is coming from the valve area, removing the thermostat does not influence the noise. Pushing the little rod on the valve with the thermostat removed only makes the noise louder.
I recorded the noise, amplified it and placed it here.
Best Answer
That's an odd noise, it sounds like something's loose inside the pipe and rattling around. Might be a piece of rust or gunk. If you remove the thermostat head and press the rod down completely, the rattling should cease because the valve is closed and there's no water flow. If the noise continues, that indicates the valve isn't closing properly.