Hi Mike,

If the sound is like a string vibrating against something, ensure that is not strings (usually G) vibrating against the bridge.

Ensure that the two screw on the saddle are well in place.

Ensure also that the vibration is not coming from a string vibrating against the frets, in that case you can fix the problem by adjusting the action and rectifying the bow of the neck.

In either case, if the sadde and neck bow are cause of vibration, try tweaking the saddles a little, and lowering the position of the saddle a bit downward. Try also to rectify the neck. turning the apposite screw.

Once you get the saddles adjusted where you want them, try just a little clear silicone on the end of a tooth pick, and dab it just under the saddle on the height adjustment screw. It is clear, and only a bit on the tip of the toothpick should do the trick. Once it dries, it's like rubber, and should keep the adjustment screws from losening up. It is easy to remove as well. You won't be able to stop all the vibrations on the guitar....it's the nature of the beast. The string vibrating in it's normal state will cause the screw to drop. It IS important to have equal pressure on both adjustment screws. Good luck!!