why is peugeot vivacity 50 whining??

i have a peugeot vivacity 50 and its whining on the back end i have looked at the back end had the wheel off n brakes etc but cant find a reason for this. it doesnt make the noise when the brakes are on n not the back wheel, but then i put the wheel on without the brakes and it makes the noise again, the bike seems to run ok but its just really annoying

mopedmad
March 2009