As Still said, it's probably slopping side to side and will need new bushings next time you haul out. It's not a huge job.
If you can get access to the top of the case with the board down, you could push a wedge (cheap rubber door-stops are ideal) either side of the plate as a temporary measure whilst sailing and sleeping - but don't forget to pull them out before trying to raise it again.
Bear in mind that a banging keel it's not only noisy but slow (you won't be winning any races with the board flopping around).
"Honestly, I don't know why seamen persist in getting wrecked in some of the outlandish places they do, when they can do it in a nice place like Fiji." -- John Caldwell, "Desperate Voyage"