He did seem pissed off when I opened his tub - I may have startled him. He was really stiff in posture when I was hearing the hissing sound - then I picked him up - he never struck at me though. I didn't know they could hiss with their mouths closed.

He was recently moved to a new rack and for the first time without hides - maybe he was just startled/scared.

I guess I will have to keep a close eye on him for a while. His temps are 90 hot side 80 cool side with at least 50% humidity.