Do you mave ANY metal to metal contacts ANYWHERE in the control rods?

Metal pushrod in a metal connector? Metal connector in a metal control horn on a surface?
Metal pushrod with ANY metal guides?

Antenna wired coiled up inside of the body? Antenna wrapped around or laying within 1" of the metal pushrods?

Rare......Try another Xmitter. Do a range check OUT DOORS. Sometimes indooor tests go wacky because of metal siding or metal heating pipes or ducts. They bounce signals back & forth ...out of time.

More rare. Change both the transmitter & reciever crystals. 1 at a time.

If none of those help.

Change the pilot.