Rozen,
It's hard to imagine MBD as I know Dudley's husbandry is all good--still using the T-Rex I presume? The only thing I can think is, is it possible he's getting too much calcium? I know that can sometimes cause twitching. You are supplementing 5 meals per week, yes? With calcium powder rather than liquid? It's hard to imagine that causing an overage of calcium. Are you feeding anything other than crickets? Any high calcium feeders such as phoenix worms? Butters? Hm, it's just very hard to say.
As to the water/mouth open/weird sounds, could he have possibly just aspirated, took in too much at once and was trying to get it down? Occasionally, our girl will gobble too many crickets at one time, and have to take a moment to open up and then chew a few times... was it just a one time thing, or is he still displaying the behavior?
I wish I had some sage wisdom and/or advice to give. Ah, and it's quite late. Most of the mods are east coasters... I imagine someone will be on tomorrow to offer more however.
I'll keep checking back in. Hang in there.
Em