I am getting a banging noise on spin, sounds like something has come off?

I have a Hotpoint WT540 1400 spin washing machine, which is making a noise on spin, the drum appears to slow when it happends and sounds like something has broken and is being spun round. Tried tightening the nuts on the balance weights and this has reduced the noise but not stopped it. I have also found what looks like a party popper with a hole through the middle, on the floor underneath and have no idea where it came from, any ideas before I get a new wahing machine?