[PsYcHe]

Could be that the caliper isn't quite returning properly and causing the discs to warp, but not too likely.

One thing may be pad deposits, often only cured by skimming the disks.

I'd try copper grease on the back of the pads as above, might help. Also find a nice quiet road and do a few 80+ to 10 mph stops, with ABS kicking it, etc.

If the ABS sensor is a bit grubby, you might get some strangeness, but I'd have thought it would just appear through the pedal, but worth checking too.