I don't know how old your machine is, but we had a somewhatg similar experience on our 30-yo Chef. Took it to a repairer (Merrills of Colchester) who found out that the brushes had worn down. He is now trying to find a set of brushes from the wholesalers.
Get it looked at!
Frank Card, Cressing, Braintree, Essex, February 2005