If the brushroll end caps become too hot it can actually melt some of the plastic that the end caps sit in and allow the brush to sit loosely in those slots and cause some vibration. Happened to one of mine and I had to wrap a small cut piece of electrical tape around the end cap so that it fit tighter in the slot and eliminated the vibration. Look into fixing it before it ruins the plastic base.
To me it sounds like the bearings in the brushroll have gone dry. Replacing the brushroll is a good idea, as is taking the brushroll to a vac shop and seeing if they can grease them for you.
When i roll the brush roll in my hand, it seems to catch a little. It doesn't turn 100% freely, so I'm sure that's probably the issue. I am stopping by the local vac shop today.