Mystery gas tank noise

[Morgsie]

Hey guys, I got a buddy who recently bought a '67 GMC 920. The truck runs alright, however there is a noise which is bugging the hell out of him. I believe this mystery noise is comming from the gas tank. Basically when you turn corners (usually the faster you're going and the tighter the corner the more audible the sound) you can hear something go from one end of the cab to the other. I've only heard the noise when the tank is near empty, but he says it does it even when full. Now I have a couple of questions:

1. Is there a baffel in the tank. If so, could it brake off and be causing this noise.
2. The gas gauge does work, which would lead me to believe that float has not broken off and floating around.
3. Has any one had or heard of this problem before.

Another buddy of mine owned an '88 GMC 1/2 ton which didn't have a working fuel gauge didn't work. He thought it was the actual gauge, so I tested it with a known good sending unit and the gauge worked fine. We dropped the tank to find that the baffel had separated from the tank and in the process took the float with it, so that's why I'm asking about the baffel. I personally think someone dropped a bolt or something into the tank, but who knows. Just wanted some input before we tear it out this weekend to see if there really is something in that damned tank!

Thanks,
morgsie