OK, thanks for that.
The most likely cause of this, is something has got between the drums.
Keep the appliance unplugged and lower the drain hose as low as possible to drain the water out into a shallow dish.
Once emptied, take the hose off the bottom of the tub.
See if you can find the item there.
If not, disconnect the wiring from the heater and remove the heater.
With a torch, look in through the heater port to see if you can find the item.
Hook it out, refit the heater and the sump hose.
Refit the belt and try the machine again.
Hope this helps
Let me know how it goes or if you need more help