loud noise from BIASI riva advance HE

need some advice please

Corgi installer fitted a BIASI Riva advance m110.32sm/c boiler with new radiators and flushed system, all done in one go last year.

Everything works ok, pressure is around 1.5 bar, temp around 60C when heating on, but the problem is a loud vibration noise form inside the boiler every 5minutes or so, this ONLY happens when the central heating is switched on, when its off there is no noise.

The loud vibrating noise stays on for around 30 seconds before going, then no noise, then 5-10 minutes later the noise back.

Bizarrely when the noise occurs, if i turn on the hot water tap for a few seconds, the noise goes away for a few minutes.

Some days its worse that others, but generally i find the colder the temperature the more frequent the noise.

all the radiators have thermostatic valves fitted, except the bathroom, which has a towel rail with no valve.

biasi engineer came out and typically no noise that day.

Any ideas please