Non-presurised system?
Go and check the header tank.
You may find the ball cock stuck well above the lack of water level.

Just done mine, and all is quiet again.
Pump no longer audible.

This is one of the simple things I keep forgetting to check :-)

Cheers

Dave R

--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

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