I've been looking at one over the past 2 days.The attachments won't turn properly at any speed.
I've just taken the gearbox apart and found that one of the drive cogs (white plastic & has the diameter of a one pence peice) is cracked and the inside should have a serated look to it but is stripped so it just slips round the shaft occaisionally catching the next cog.
could be that yours is starting to do same. the biggest problem is taking the top of the gearbox off to check it.
Ness
March 2008