hot water grinding noise

[PeterR]

Hello, when our hot water comes on in the morning and evening there is a deep grinding noise which lasts less than 5 minutes and then stops. After that, all is well. We have a combi boiler.
Thanks.

 

[Deleted member 120897]

So a Combi boiler works by hot water demand (usually), so when you say coming on, are you opening a tap?