RE: Unusual interference
A couple more suggestions:
A Hobbico frequency checker is a worthy addition to any field box. Tower has them for $39. It showed me what my glitches were cause from. Looks like ch50 is a bad one at my field. It doesn't sound like it'll fix this problem, but still worth considering, at least you'll know.
I know it's a low wing, but is there a way you can exit the antenna wire immediately out the fuselage and tape it to the tail for testing? Maybe poke a 1/16" hole behind the canopy? Simple is good when your trying to troubleshoot something. Then you can go from there. That way it's parallel to nothing and as far from everything as possible.
Try a different battery and switching the elevator servo with the aileron or throttle servo. It MAY not be a radio problem.