Horizon T101 Treadmill squeaks loudly with each step while running about 8 minutes into the run and get's exponentially worse. It also squeaks if I have the machine off and am just lightly bouncing on the deck. Does not squeak while walking.

SOURCE: with every step I get squeak / chirp while running on treadmill.

Check the knob used to hold it up in the folded position. While running, have someone pull it to the out position. That was the problem on mine. If it is, a little grease on the end of the rod should do it.

SOURCE: Horizon treadmill loud squeaking sound

you need to lubricate the pivot points and deck. Check to make sure the deck is not broken.