Sounds like someones been playing a bit too much Deadspace. I've had the best luck with them in chests, honestly. The Pirate's Booty chests, chest at the end of hero's pass, etc. They also seem to drop quite a bit from Ultimate Badass Varkids, which I noticed when trying to farm for Vermivorus.
A lying tongue hates those it crushes, but a flattering mouth works ruin. -- GT: Wretched Owls
I almost always have an E-Tech pop out of a certain chest...I wanna say it's the ones at the end of Southpaw. When I was farming for an Emperor I'm not kidding like 9/10 times the chest at the end would have an E-tech of some kind in it.