RE: Spectrum servos on 72 Mhz?
I use the spektrum ds821 servos on 72 MHz without problem. I'm using Futaba TX and RX.
It seems to me the common denominator is your 72 MHz gear. And since others have used these servos with 72MHz, it makes me wonder if you've got an RF noise problem wreaking havoc on your 72MHz gear and the servos are not part of the problem, just showing a symptom. Try hooking up different servos and repeating the test to see if they go nuts. That would be proof that you have a general problem with RF noise when the engine is running.