RE: servo jitter/glitching but this is different, vey strange !
Possibly both servos are bad - or possibly a faulty connector - is it connected to a Y lead?
I had a similar experience recently on a foamy where I couldn't get a range check of any type on it. I changed receivers a couple of times, batteris and it was all because of a faulty plug on my aileron Y lead. the pins would move to almost touch each other when it got plugged in. I replaced the lead and the problem was solved