Why there is a strange sound coming from Smart Radiator Thermostat V3+ ?

coogito

I have several V3+ Thermostat but one of them is making strange sound the same as can be seen here on the video https://www.reddit.com/r/tado/comments/q77ufe/what_is_this_sound_and_how_do_i_make_it_stop/

Any idea how to solve it?