how do I replace the heater on my Bosch wff2001 washing machine?

I've replaced the heater on my Bosch WFF2001 washing machine. Seemed to go ok although the old heater was difficult to remove. I was not sure about one thing. Inside the main drum housing there appears to be a clip that either acts to hold the heater down or to keep it away from the housing. Any ideas which? It is extremely difficult to get at and the only way I can see is by removing the rotating drum. I do get some knocking on fast spin so I suspect the heater is hitting the drum and should be held down.