Hi,
last December my daughter had a combimate installed along with a new Baxi duo-tec 28 he boiler (this was a completely new CH install)
A quick test seems to rule out noises from the boiler, but the combimate does seem generally noisy (though not alarmingly so)
I'm suspecting maybe an air lock somewhere, but thought I'd see if anyone else has had instances of noisy combimates.
Thanks!