Navien combo unit .. noise with video

[Loucampy]

Was wondering if anyone knows what noise this could be from...
Its a combo unit 2 zones attached
Only happens when the unit comes on for heating the house..

does not come on during hot water mode....

This is a YouTube video of the noise

Thanks again for looking

 

[Bannerman]

I suspect the water circulation pump for the heating loop. I further suspect a pump motor bearing but could be although less likely, something internally which is in contact with the pump impeller.

To identify the source of a mechanical sound such as that, a screwdriver tip held firmly against various suspected components, will transfer the noise through the screwdriver's hard (not cushioned) handle. Placing your ear against the screwdriver handle will usually assist to pinpoint the location where the sound is loudest.