knocking sound from drum area?

Whrilpool AWM5145, After doing a hot wash for whites, the machine started to go into spin cycle then it started making a loud knocking sound as though something was loose inbetween the metal drum and the plastic case, it continued making this noise and got worse during the fast spin, after the wash, I removed the top and spun the drum and it sounds like something is either loosed in the void between the metal drum and the plastic case OR one of the heating elements is broke? I removed the outlet pipe from underneath and could see the element, but could not see anything other than that, any ideas as to the possible cause?

G Morgan
May 2011