The title explains basically the sum of it, but basically when i let off of the gas my car rattles for like a split second really loud.

And the thing that confuses me is that it goes away sometimes, sometimes it doesn’t even happen and then sometimes it happens a lot. It makes me a little nervous and i’m going to take it in once i get the chance (i have headlights and a fender to replace)

I thought it was when i pushed my clutch in but then noticed it happened when i let off the gas, my clutch also rattles a bit but i think it’s because of a lightweight flywheel the last owner put in.

Does anyone have a clue what this could be?

 

Rusty catalytic converter heat shields are the most common rattle especially on change of RPM. Do a search and you'll find threads where people talk about how they try and deal with it like clamping or removing etc. You might be able to just bang on your y-pipe with your hand while the car is parked and cold and cause a little of the same kind of rattle to confirm if that's your problem.