Well, my frustrations continue. The source of the interference is still eluding me and any more suggestions would be appreciated. Below is a list of what I have done to date none of which corrected the problem. Yesterday, I remove the engine and put it in a test stand. With the engine running, and the plane held a foot from the engine, there was no interference! This leads me to believe it is a vibration-induced problem in the remaining components of the plane, which there aren’t many.

Big Bird asked the question “Is the throttle push rod non metallic?” No it is metallic 6” long rod, but there is plastic clevis/ball socket on the throttle and a plastic control arm on the servo. Shouldn’t that be ok or could the metal rod by itself be a problem?

Chuck

By passed the switches for both the ignition and radio
Tried different batteries for both the receiver and ignition
Moved the ignition battery about 2’ from the receiver
Moved the receiver five feet away from the plane; this lessened the interference, but not much
Disconnected all the servos except the throttle
Disconnected all the servos except the rudder and manually adjusted the throttle
Switched receiver
Took off tail feathers metal bracing
Removed center upper wing section and rigging wires
Cursed