Weird glitch?

yes its not a glitche just a little bug. seen it millions of times

seenn itttttttttt

that happen to me in 50% of all my games
but i ignore it

This happens to me every time someone dies while not shooting and standing still (At least from what I have noticed). But also have any of you ever had a black box above everything else like a wallhack but it is not a player, it's like a black 3d box. I think it might be my suckish graphics card.