Almost certainly the carbon brushes, just normal wear. Very easy to replace. Explains itself when you have the brushes and replace.
Unplug the machine and take of the top lid (philips screwdriver, push back) and look at the front of the motor.
Unplug the two outer wires. Those are connected to the brushes (two brushes one wire to each), they have white cover.
Look at the sides. With a flat screwdriver push the latch that is to the back of the white brush cover and slide it out.
The rest is self explanatory.
F.R.Ragnarsson, March 2008