Eco bubble clicking/chugging engine-like sound when heating water (and drum is still)

My (newly bought) Samsung Eco Bubble washing machine (model WW80J5456FX) makes an unusual sound – like a soft engine rumbling, chugging or clicking inside – in the initial stage(s) of washing, when the water if being heated up. It is not a particularly loud noise, but it is slightly unsettling, especially as the sound is made even when the drum is NOT rotating. So this engine-like chugging coming from inside the machine is heard even when the machine is perfectly still, while the water inside is being heated.

Has anyone else encountered that? The sound in itself is not bothering me, but I would like to be reassured that this is not a defect or a flaw of the machine. (And the Samsung customer call centre has been frustratingly useless).