Can you post the model number of the appliance please?
Does it clunk if you turn the drum manually?
Does it clunk if you run the machine empty?
OK, thanks for that.
Look into the drum and at the rear centre.
You'll see the rivets holding the drum shaft to the drum.
Turn the drum and watch the rivets.
Do they wobble/move?
Unplug the appliance, take the top off.
Lift the rear of the drum, does the drum "jump" as you turn it.
The "jump" should coincide with the clunk.
Are you looking to repair this yourself or are you looking for a price for repair by an engineer?
If you go to www.repaircare.co.uk you can get a quote for repair that includes parts and labour.
They will either fit a new drum or a repair kit for the drum support.
It really depends on how bad the drum is.
Given that the average repairer labour/call out charge will be around £70 it doesn't need a lot of parts to push the repair to over the £120 mark.
Check the quote and you'll be better placed to decide on whether to repair or replace the appliance.
Comet also do a fixed price repair at £125.
Click here for the comet deal
Hope this is of some help
Let me know how it goes or if you need more help