Any ignition system on a model engine, be it magneto or electronic, will emit electronic noise (RF) while it is operating.

If you put a piece of metal wire, like a metal pushrod, in the vicinity of this RF interference, the wire will act as an antenna and radiate this "noise" along its length.

At the other end of this wire is usually a servo and that is connected electrically to the receiver.

See where I'm going?

Use plastic clevises at the engine and non-metallic pushrods back to the servo.

Just my opinion, but it seems to reduce or eliminate radio interference from ignition systems for me and a number of others too.