Hi N,

Sounds like the rotor might be slightly bent. This happens to me
occasionally; I live in an area with a lot of sticks which quite often get
tossed into my wheels - sometimes hitting and bending he rotor.

My solution is to spin the wheel, look in the caliper and see where it's
dragging. Usually a few presses by hand on the high side bends it right
back.

If it's not bent but still dragging on one side, what works for me is to
loosen the caliper mounts, apply the brake and retighten while holding the
brake lever. This tends to center it perfectly.

If it's *still* dragging, your calipers may not be retracting - I suggest
you then refer to the service documentation for your brakes.

Good luck.