What can knock in MacBook Pro 2014 Late Retina?

Question

macbook

I just accidentally pressed hard from the bottom of the case (I just lifted the poppy with one hand from the top right) and when I sat down I heard a knocking sound. If you shake it again, then the sound appears for a couple of seconds and if you do not change the position in any way, it disappears. The sound can be heard here (), you can hear it right from above

Well, it can’t be that this is cooling (as I understand it is on the left)

UPD: the sound disappeared and does not appear after I wrote a post and tried to record sound. I'll try to describe it. Take a fly and put it in a jar with plastic lids. Seems to describe correctly

Answer 1

What can knock on a MacBook Pro

Carburetor.
PS Seriously, nothing but the cooler can knock there. Apparently, after all, something bent and began to hurt.