This is a random enemy spawn, I've seen two (on 360) at level 6 as a skag and a spiderant (level 34) . For PS3 I ran across this guy as a Rakk (level 24)
You'll know its a chubby right away when you see it, it will be bloated (full of loot) they're usually a level or two higher than your current rank, but arent too tough. Kill them and this will pop...er....quietly appear a few seconds later in the top right corner.