Clutch/brushroll?
If you recline it as if vacuuming (and it squeals), does turning the clutch to 'off' stop the noise?
If so, then take the brushroll out, take the end caps off, clean it all off and put a few drops of oil on the bearings. If it still squeals, then it's the clutch. That's either a strip down and new belts job or a new clutch depending on how you feel.