My Hoover 500m has a grating noise on start up of agitator?

Purchased 2nd hand-appeared to work but did not try full cycle or on high level-trying to save water & seller's time. Got it home,cleaned it and bought a cleaner-rubbidin washing machine magic to finish the job. This says to fill to maximum level and longest cycle,run for 10 mins,then pause and leave- At this point the inner & outer bowl had sagged well below the top hob. However after 2-3 secs when agitator started there was a terrible grating noise and turned it off. Pumped water out,both pumping and spinning were faultless. Where should I start?