My dyson cleaner keeps squealing really loud, checked the belt, it looks fine

Try taking it apart and see if you can oil the motor bearings. If you can you will need high-speed oil which is sold at all HVAC supply stores in a plastic bottle with a long plastic spout. It is for oiling all types of motors and AC/heating motors. It could also be another part, but there's no way to know without taking it apart.