I had same symptoms so I disassembled the head and there is a small Torx screw inside the plastic piece that spins the brush (pointed to in the picture below). After you remove the screw then you can pull the plastic piece off. There was a lot of hair that had gotten underneath that brush driver and once I had it removed the motor could spin a lot easier and the problem was solved. When putting the brush driver plastic piece back on don’t overtighten it. Check the spin is good.
[image|2275715]