Hi wheezy,
I was able to solve this same problem on a friend's disc-equipped derailleur bike recently. His cones were properly adjusted without play. Like yours, his disc only rubbed/squeaked when he pressed down on the right pedal. This was a clue the rubbing was torque-induced. As it happened, there were two problems that caused this:
1) A simple removal and reinstall of the wheel showed the QR was fine for securing the wheel, but allowed a minuscule amount of movement of the hub in the vertical dropout under load. Tightening it took out most of the rubbing. His pads were set a bit close, and the wheel wasn't perfectly even in the slots. It didn't take much to put one pad too close to the runout of the disc.
2) While the bike was in the stand, I centered the caliper by loosening it, then turning the cranks, leaving the bolts slightly loose, then tightened them up while still turning the cranks.
This did the trick. Perhaps there's something in there that might resolve your disc-rubbing issue, too.
Best,
Dan.