Banging noise - indesit vented tumble dryer?

I put a large wet cushion in my drier and it wasn't happy - got water all over the floor and banged a lot. I've used it since and it dries (with no water on the floor) but when it heats up there is a loud intermittent clanking noise as the drum turns. I've checked and the filter and outlet hose are clear, and there is nothing stuck in the machine. What is wrong?