v-minion - rattling noise

Hi! I could not figure out what is the source of this horrible rattling noise.
I was thinking it is a fan shroud (was not flush with back plate), reprinted and reassembled the whole EVA - but it is still there.

It feels it might be a X rail. Printer is second hand, so I don't know what is the rail quality and what happened before, but rails are RR stock ones I think.

Any ideas?