Since I put new rotors on my CX bike (replaced the Deore-level rotors with XT ones), the rear one is not quite right.

It "grabs" at a regular point every rotation...either that, or a point opposite is "slipping"...hard to tell. Whatever the case may be, it creates a grabbing/pulsing effect.

I've sanded it, and cleaned with rubbing alcohol. The rotor appears to be true as well.

It's "bedding in", so it is starting to show marks/wear from the pad, but I can't visually detect any irregularities.

The brake is a mechanical Avid BB7.

I'm at a bit of a loss now. It certainly doesn't stop me from riding, but it is irritating. And it has diminished the usual advantage this bike has in wet weather. I was coming to a stop the other day, the front brake was modulating normally, and the rear brake "grabbed" at that point in the rotation, causing the tire to momentarily lock and make the back end go squirrely.

Thoughts?