hmmm if you locked your phone in there in the past and didn't have this issue then it probably isn't that

you do have some CPU usage there. If the phone maintained a low signal 3g connection live for 4 hours, then that is normal

imaging talking on the phone for 4 hours in a place with bad 3g reception, this is what your phone was doing

i don't think you should worry about it. Unless you absolutely need your phone to be connected on the net, you will be much better off disconnecting from the internet and switching back to 2g when you leave it in the locker.