Well, the inside of that nozzle is caked with crudmeaning it has sucked up some wet sludge and it dried there. Looks like you have a Power Nozzle makeover project.
First you gotta check it isn't the belt rubber doing the squeeking on a frozen motor axle. Then ya have to remove the brush roll and check the bearings for accumulated treads/hair/impacted dustbunnies. Once you have the brush roll spinning freely in it's bearings then you have to thoroughly test out and diagnose the motor. You didn't say if the brush motor is turning freely.
1. does the armature turn easily by hand? - shot of machine oil.
2. does the armature turn sluggishly? - shot of rust penetrating oil and turn by hand for a while till it spins.
3 does the armature turn and wobble in its bearings? Bearings shot.
4. is the armature frozen in place and will not turn? Shots of penetrating rust oil, use vice grips on axle to force the armature to turn. Repeat repeat repeat until the armature spins. Take the motor apart and Emory paper/steel wool the shafts.
2/3/4 (or something that got jammed in the brushroll once causing it to stop) will cause the failsafe breaker to trip allowing no electricity to flow to the motor until the reset button is pushed. It could very well be a loose connection to the circuit breaker.
Yeah, that nozzle is filthy and no doubt some of that liquid crud entered all sorts of places it shouldn't oughta...like all along the suction path into the bag.