Boiler whine

[a9blue]

I have a Baxi condenser combi less than a year old.
For a while now there has been a high pitched whine when in heating mode.
The noise goes away when running hot water but returns as soon as tap turned off.
Also it's not as bad when all radiators are fully open.
Can anyone help,advise?

 

[McCombi]

Do you have an external bypass fitted or is there a rad with no thermostatic valve fitted to act as a bypass?

Remove one trv from radiator and if it stops the noise a bypass is needed or one fitted already needs adjusted by the sound of it.

 

[a9blue]

The bathroom towel rail has no trv.