Looks like the motor’s just reacting to the power‑line ripple that the radio amps are whipping up. First, confirm the grounding scheme: is the motor’s chassis ground tied directly to the amplifier chassis ground? If that link is loose or high‑impedance, the motor’s reference voltage will wander as the amplifier drives more current, and you’ll see those hiccups. If the ground looks solid, the next culprit is signal bleed—your antenna is probably coupling RF into the motor’s power leads. Run a short, twisted‑pair cable between the motor’s supply and the amplifier’s power feed, and add a ferrite bead on the line; that should choke the high‑frequency noise. In short: check the ground continuity first, then add shielding and ferrite isolation on the power feed. That should turn the hiccups into a quiet, steady spin.