DavecUK
The rumbling sound and the other sound were together and not ‘outside’ noise. I think the ch! ch! was a bit like a noise as the water was ‘popping’? A ‘sort’ of noise you might get when water is splashed on an electric stoves hot hotplate.
It’s just I didn’t think either noise was audible all the past week or so, but I might have missed hearing it as I wasn’t with the machine all the time it was being used previously.
Edit: according to AI Google the Lelit machines can make different noise during fast heat up! The noise is happening as the boiler builds pressure and the boiler anti-vac valve opens?
But thanks for listening and reassuring us @DavecUK :)