Dyson DC35 -works but intermittent (Maidenhead, SL6 4)

Old dyson stick vacuum.
It works OK, but something is wrong meaning it sort of 'revs', rather than making standard sound and sucking consistently.
Someone on here may have knowledge of how to fix.
Power cable has been shortened. Needs a good clean.

Preference to those who state in their response when they could collect.