No clogs, work fine, but makes a very loud wailing sound? what could it be?

My Dirt devil Reaction does the same thing. So I took apart the motor and it was crammed w/ dirt then I decided to clean it out. next time I vacuumed my house it was a lot quieter. The guy from Jones sew and vac said baggless vacuum filters most of the time fail and let dirt get in the motor and start to scream. I read a lot of things saying Dirt devil Reaction is the most common vacuum to get dirt in the motor and start to wail then get worse & worse and get to the point where they start to almost scream. P.S if you let it scream for along time of use it will give the motor permanent damage and you will smell electrical burning, if that happens it will be too late so you will half to buy a new machine. To get to the motor you can take the dust contaner off and take the black filter then use your down stairs vacuum and get a small attachament and stick it in and vacuum it out,if not have two vacuums borrow one. If that doesn't clean it out you will need to take all the plastic appart and realy get to the motor good. If my advice dosn't help it is ok to still use it, it will just be loud until the motor of it is totally fried. This should work it worked on my Dirt devil Reaction. I'm sorry if it doesn't work out. :D

Mine also wailed alot just as the beater brush drive belt wast about to break

The carbon brushes on the motor may have either went bad or need to be reseated.