actually we had the same problem. What we did was to put an aircraft nut on it. This was so that no matter which way they ran, the screw and nut where not undoing themselves. Remember that saying righty tighty lefty losey, well basically charlie was run to the left, and undoing his screw everynight making tons of noise. We also have our chins in our room, for it is the coolest room for them.
Hope this helps!! If you dont understand ask a hardware person...they may be able to help!!!!
-Sarah