My impeller slides on the shaft too. its supposed to.
Is it a grinding sound? Mine does it too but only when theres a partial blockage of the air inlet. Pull it off and check for a buildup of calcium on the internal side. You may need to poke a screw or nail in from the outside to clear.
Yep, Ran about an hour in some bleach and she's as good as new! Bleach just destroys everything...coraline, gone! Nasty green, brown and red crap, gonzo too. Best part, no elbow grease required yay Me!