If the brushes make a 'ratcheting' noise as soon as they start rotating then it sounds like the clutch mechanism. This generally occurs if there is something (possibly a piece of string) catching/jamming the rollar bar. You should be able to rotate the brushbar by hand. If you turn the Dyson over you can take the sole plate off of the brush bar which should allow inspection of the brush bar. I think 3, possibly yellow, plastic screws hold it on: you can use a 2 pence piece to remove the screws. Once the sole plate is off you will be able to clean around the brush bars. The full assembly can also be removed by gently stretching the drive band for cleaning. If this does not cure the problem then it could be the clutch mechanism at the motor housing. Hope this helps.
Martin, August 2005