It could be the belt starting to fray and the bits getting into the drum... I have just had this exact same issue...
My belt had practically worn threw and there was a black dust all over the back of the drum as I took off the back...
I have bought a new belt off ebay and fitted it...
Need to be DIY savi and have 8mm socket to undo the machine!
Good luck
NoProbs, October 2011