That is definitely a loose something. it does not sound like its inside any
water containing parts to me. It could of course be almost anything. The
boiler sounds pretty noisy to start with, was it always that noisy? If not
you might have an issue and it just happens that its making a piece of metal
vibrate.
Was the pump unseated or moved. Often the mountings have a lot to do with
the transfer of vibrations to the structure and the loose bit you hear might
have always been there.
Brian

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This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"RJH" wrote in message
news
Can anyone identify this noise? -

https://drive.google.com/open?id=1o_...flq4qiwX_jS6vh

It's a sort of high pitch metallic rattling, happens all the time, and has
started since I drained and refilled the closed combi system.

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Cheers, Rob