FX M3 rattle is it this normal?

Hello everyone just a quick question. I bought a used M3 never had experience before. I notice when I point muzzle down then quickly up there is a rattle in the middle of rifle. Sounds like something is loose like the hammer spring and hammer. I heard that this is common.
when I cock the rifle/bolt back and I again shake the rifle the sound disapears.

Is this normal to have this rattle? I can live with if I know it’s normal? If it’s not normal how can you fix this???