I have a friend that worked for three months trying to get rid of is interference, he finally broke down and went the PCM way and it works. I know that the PCM is just masking the problem.

It was a strange problem though, everything was changed out of the airplane, servo's, wires, batteries, ignition ect... The best idea that we came up with is that he has a tight bearing that is squealing in the RF range. In a few months he will try the PPM reciever again to see if the problem still exists.