A glitch is any unwanted servo movement. If using FM mode you will see it when it happens. Start by looking at the obvious (loose connections, ignition if gas, any metal to metal connections). It is made when noise is introduced to the receiver that breaks the s/n (signal to noise) threshold, and is passed on to the servos. That's it in a nutshell. If you want to get deeper in the subject, just google glitches. I'm sure you will find a wealth of information.

Bob