I agree on the metal pushrod, get rid of it.

Also, what type of engine and ignition are you running? I have a Fuji-43 that would interfere really bad. I had everything set up "right" but couldn't eliminate the problem. Finally, I installed a new ignition from CH and the problem was solved.

The whole thing about 2.4GHz being immune to interference is not necessarily true. It is far less prone but if something such as an ignition is producing just the right frequency, the receiver or possibly the servos can pick it up.