My Dirt Devil bagless makes a loud squealing noise when I vacuum.?

It’s most likely the motor. I realize that most people hate to buy and change bags in a vacuum cleaner, but they don’t realize that the bag is actually the largest filter in the system. Good bags will trap nearly all the dirt and pollen and allergens, and every time you change you get a fresh filtering system to start over with. In a bagless cleaner, there are at least two, usually three or more filters to accomplish the same thing the bag does. Unfortunately most people don’t feel they want to invest in a new filter when the old one doesn’t look bad. It can be nearly completely plugged and still look great, and it’s nearly impossible to thoroughly clean one of the pleated paper filters. One of them usually costs as much as a couple of packs of bags. So the cleaner is used with a filter that’s mostly plugged, cutting down the available air flow that’s needed to cool the motor properly and pretty soon you have burned out bearings or an armature that’s overheated and burned the commutator. If the squealing noise winds down with the motor, that’s probably it.

When you have the belt off see if you can manually turn the motor. make sure that the beater brush isn’t full of hair or wire or even staples.
see if anything is caught up in the motor and clean out all hoses. if it still squeels. then have it checked by a service store.

either the motor is bad or you have something stuck up inside.look at the underside and see if there is paper or paper clip stuck in there.you might have to take the bottom off and see whats really going on.take the brush roler off and the belt and then turn it on and see if it does the same thing