Well, I had a car in the shop today making the noise sparky13 describes.
Thinking it was probably a broken fuel pump module, I pulled it out to
check. Guess what? Everything was intact and I found nothing rolling
around in the tank.
In fact, considering the discussion here, I figured this was a common
complaint by now and called Hyundai to see what their official position
is. According to Hyundai, the fuel tank has no baffles and the noise
occurs because the fuel actually is sloshing around and is normal.