I've got two steppers which are running rough. Here's a vid.

http://users.actrix.co.nz/dougal.ell...er%20catch.wmv

This is the worst, the second isn't so bad and the third one runs perfectly smooth. They are all 280 oz-in 8 wire dual shaft nema 23 motors. I've pulled the end caps off this one a couple of times and can find no sign of internal conflict.
The motors are new, bearings are good and they spin smoothly by hand. But when running they're rough. This one catches every 2-3 revolutions and in the same spot forwards, a different spot backwards.

Has anyone had a similar issue?