Mine would only "vibrate" if i was doing something to it that it didnt like. Removing a stuck shed on a spike, removing a feeder that was on the cham, etc. I think its "i dont like what you are doing but this is the most effort im going to put into stopping this".
My female will do this when she wants me to drop her. The vibration is meant to over stimulate the predators senses so that you will drop the Chameleon. It’s an amazing defense Mechanism
Closing of the eyes during handling is basically the Chameleon accepting that it cannot escape. Made the mistake of thinking it was a sign of comfort once.. Beyond glad I found the forums before long.