I think Greg is on the right track, motor noise or equivalent. Your transmitter works fine with the single conversion receivers I would think it is OK. Double check the capacitors and diode (if any) on your motor did you follow the mfgrs recommendations exactly? Is a capacitor chipped or cracked? I hope you have short leads from your ESC to the motor.

I am a newbe with electric flying but a very oldbe with electronics. Good luck