Wow, it's been a while since I posted here. I'm still on my original D1, unrooted (and no task killers). This problem popped up about a week ago, and I've had the damnedest time trying to figure out what's going on.
It started out when I noticed that a) my battery life had plummeted suddenly, and b) my phone was getting very hot (battery temp ~105F or so) even when unplugged. These two led me to think that some app was running in the background and just churning.
I checked out battery use, and Android System seemed abnormally high. Upon opening it up, I saw that Data sent was up around 60M since last unplugged (which was only a couple hours). What the heck? It was in my pocket, I wasn't even using it!
Over the past week, I've noticed the same behavior - huge amounts of data constantly being transmitted at all times (even through wi-fi if I connect to my home network), heating up the phone and eating battery. It's been so bad on the drain that sometimes even the charger can't keep up, and the battery slowly drains while I'm charging! I put it in airplane mode to cut off data transmission in order to charge.
The only new apps I've installed within the past month are Words With Friends and ArchiDroid. Is Words With Friends a known offender of insane data transmission? And if that's the case, why does it show up under Android System rather than WWF?