Whenever one of my vac’s is sounding like it’s reving too loud and working too hard when it shouldn’t, it is clogged somewhere. Check the air path from start (beater bar area) to finish (bag). Paper clips, nails, small wood chip, etc, all can easily get lodged somewhere and plug it up as hair and other stuff try to pass bye. Since you said you already did this and it isn’t clogged, may want to call Big John. Only other things I could think would possibly be that the bearings on the beater bar aren’t allowing the bar to spin, or maybe a belt is going out.