It could be a number of things but my advice would be to contact Manchester Vacs 0161 371 1090 or see their excellent website. I have a DC07 and have been able to repair most parts (motor, brush, clutch, various body parts etc). New or reconditioned parts are sent out immediately and are good value.
StringWells
April 2013
I can answer this question...
my dyson D07 makes a screaching noise when the brushes are down?
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix vacuum cleaners.