"Whirr" suggests going faster - higher pitch sound. Does the pitch rise in frequency (whirring and going faster) or does it drop (droning and going slower).
My old Flymos have had motor problems after 5 years or so - the brushes wear out - motor runs rough or smokes a bit - the motor runs slower and the pitch drops - search on here for FLYMO.
Find out how to access the top of the motor - run the machine until it begins to complain - REMOVE THE POWER and access the motor - examine the brushes feel around for heat. There's not much else to go wrong apart from the motor.
Richard Buxton, October 2008
