http://www.neighborhoodies.com/mummra-tee-p-331.html
It’s funny, except I’m not sure what sound they’re talking about.
I’ve heard a lot of things come out of Mumm-Ra - but I don’t remember any of them sounding like THAT. lol
I know what it is - it’s the noise he made after he transformed and getting beaten up. I think so, anyway. 
Which episode? (or is this during more than one episode?)
Which episodes? No, he’d do it generally at the end of his transformations or whenever he’d get beaten (although this only happens in some episodes). I think so, anyway. Could be wrong.
Could be from the intro as well.