Clicking from rear wheel – new MTB

Does anyone have any idea what might be causing this ?

EDIT : i was leaning , chest against saddle full force to reproduce the issue , also i am 117 kg 198 cm .

I took it for the first service today they tightened spokes and all that, but still makes the sound , will i always have to listen to that ticking bomb?

Was there damage caused somehow so soon? I dont do mountain biking at all, i only ride in the city.

Is this grounds to return it or seek wheel replacement? Is it related to my dimensions meaning only very expensive wheels wont do that ?

Thanks in advance.