[BrianG]

It is possible the motor is electrically noisy, but the metal motor can does offer some sort of shielding. I would suspect the wires to the motor before anything else. As far as the chassis goes - I suppose it is possible to induce a voltage in it, but it is quite big and not exactly an ideal "antenna".

Instead of shielding the motor, I'd shield the more sensitive parts; like the wire(s) from the Rx to the ESC and/or the Rx itself. Shielding the motor might reduce its ability to dissipate heat.

Also, metal gears rubbing on each other produces noise; I've heard that is why you will rarely find a servo with all metal gears - one will be plastic or metal coated plastic. Does your tranny have all metal gears and are any wires right next to it?

Something else to look at: Try not to run wires parallel to sources of noise - especially the Rx-to-ESC wires. Try running them perpendicular to each other if possible.