[BrianG]

Looks like a clean setup so a wire mess is not the issue, and the wires are already far away from the radio stuff.

I wonder if shielding the wires would help? For a quick temporary test, wrap some tape or something around the motor connectors (for insulation), then wrap some tin foil around the motor wires. Then, if possible, use some extra wire and tie the tin foil to ground. This is temporary just to see if it works, so it doesn't need to be pretty for now.

Are you running metal on metal gears in the tranny? Metal on metal gears can cause some RF interference sometimes.

On an unrelated note; I don't see a UBEC? You should be running a UBEC on the MM...