[Dog Gone]

If this is correct, then it's down to a fuel tank problem (do these planes even have a center fuel tank?) or terrorism. I can't think of any other possibilities, other than a seagull biting off the tail as mentioned above.

[Cool Guy]

I would think along the lines of, sabatoge before take-off, on-board explosives or just a good ole SAM.

[r9etb]

If this is correct, then it's down to a fuel tank problem (do these planes even have a center fuel tank?) or terrorism. I can't think of any other possibilities

I recall several years ago a story in the Seattle papers about a B-52 at McChord AFB. The crew had just flown in, and were walking away from the aircraft when its wing fell off. It just broke off at the root. There was even a picture in the paper -- it crushed a piece of ground support equipment.

Fatigue effects could explain this accident, too. The point is: there are plenty of plausible mechanical failure modes. "Air frame rattle" could indicate trouble at the wing root, and a wing failure, and the possibility of fuel and electrical sparks in close proximity, are consistent with the reports of flames at the "armpit" of the aircraft.

[colorado tanker]

Third possibility: human error/stupidity in not reconnecting or properly connecting a part during maintenance. It's a long shot, but sometimes Murphy's law takes over. Fourth possibility: structural failure due to manufacturing defect. I agree your first two are the most likely.