White Knight SensorDry making noises when drum spins?

Tumble dryer making loud rubbing noises when working. Like something is stuck. I can see something white at the back throught the holes when looking inside with door open. I have taken the back off and exposed motor, not brave enought to take motor off to expose the next bit, back of the drum probably. Once I cleaned all the fluff out of filter and hose it seems to only make the rubbing noise sometimes. Is it easy to get to the back to see if it is a tissue that is caught, or is there meant to be something white at the back?

The drum is spinning easier now than on saturday when it statred making noises, so something must be caught somewhere. how do i check???

Oh, and i've lost my manual, so appoligies if this would be covered in that.