Bruce.
Sorry for lack of reply, been offline for a while. It would appear that something (servo leads?) is picking up co-channel or other airborn interference at the field. You would not get this at home. Have you got any Ferrite Rings (like the glider boys use on long leads in wings etc ?)
Twisting the leads may help, but Ferrites might give better results if this is the problem.
Have you had any joy with your investigations?

Ian.