I've been told I mumble some times. I blame it on switching between three spoken languages daily though. Not being able to properly pronounce the words quick enough, I tend taking shortcuts, and then happen to mumble a bit more than most people. Not always, but enough that people I interact with often will notice.

And on the point of switching between languages constantly, I've noticed myself loosing a bit of my pronunciation and vocabulary of my native tongue. I blame it on living and working abroad for 8+ years. Makes sense I guess, but still annoying to myself...