I think there's supposed to be some metal clips that the screws go through.
Does it have an aftermarket stereo in it, or is it stock?
If it's stock, and nobody's been in the dash, you can bet you'll have to rig something to make it stop rattle/buzzing.
If it's got an aftermarket stereo in it, you can bet something was left out, installed wrong, broken or misalligned when it was put back together.