Just fixed the same problem with my UM2.
A piece of filament was in the feed unit on the back and was causing me pretty much the same problem.
I dismantled the feed unit and out came a short piece of filament about 1/4 inch long, now it runs fine.
Note that you have to remove the inside cover to hold the stepper in place while you reassemble it.
And the wires want to get pinched under the stepper when when you put it back in, just hold them out of the way while reinstalling the stepper.
good luck hope this fixes yours as it did mine.