Avid mechanical brakes tend to go out of adjustment pretty quickly. I would suggest realigning the calipers first (loosen up bolts, use red knobs to grab disc, tighten mounting bolts, back off pads). Then make sure that the disc isn't lined up too close to the inside (could be hitting the caliper instead of the pad). Get the inboard pad as close as possible to the disc without dragging. When you grab the brake lever the disc should not deflect very much at all. If all that doesn't work, try the kool stop pads.