I have a Kenmore progressive cannister vacuum cleaner.

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I had a vacuum cleaner that did the same thing. My vacuum had three suction levels. The noise level would decrease as I lowered the level. I also noticed that when I turned the vacuum off the sound didn't stop instantly, it wound down/faded off as the motor slowed down. I found the problem to be the bearings in the main motor. I've been told that the motor that powers the carpet brushes can also make the sound if the motor bearing fails.

go to this link and you should find the manual,scroll down to the bottom of the page and you should find it,this might help you get it sorted. Kenmore Progressive True Hepa vacuum cleaner manual Google Search

check the reset button or the wire that goes into the powermate sometimes it frays and breaks

You are correct. The belt is supposed to go around the peg that is connected to the lever so that when it is on the Floor /Tools setting the belt is not driven by the drive shaft.

You need to open the head by gently squeezing the light cover housing and lifting it off. There will be two screws underneath and once removed the lid will lift off and reveal the area where the pedal installs.

How to Repair a Vacuum Cleaner
http://home.howstuffworks.com/how-to-repair-small-appliances8.htm

You can check for the manual at:

www.managemyhome.com

I would suggest checking the hoses for clogs. Especially the hose right after the carpet brushes. Don't forget to clean off your brush. Hope this helps.

The switch in the hose maybe bad, motor problem, or some of these cannisters have a relay mounted by the motor, it may be bad.

Check the plug ends at the top of the wand and the plug going into the hose handle, also at the bottom of the wand. It sounds like they may be burnt, if so they will need to be replaced. One cause of these connections going bad is not turning the power head off when connecting or disconnecting. Therre are other causes, the switch in the handle is going bad, also some of these cannisters have a relay mounted by the vac motor, sometimes they go bad.