Its glitchy when you get about 35 yards from the plane with the antenna down.
Well, that's 105 feet which is about normal. Does the glitching stop if you extent the antenna?
It seems to be most prevalent at lower RPMs.
It doesn't really sound ignition related if it's mostly at lower rpm's. The plane is gonna shake the most at lower rpm's, maybe some component is being affected by it. I'm assuming the range check is OK with engine off?