The baffle is the board that the speaker is attached to. On some amps the baffle is attached to the cabinet with screws. On other cabinets is is glued into place. If a screw is loose, the baffle could vibrate. On older cabinets, sometimes the plywood laminates around the speaker cutout become loose and the laminated vibrate. This causes a buzzing under certain conditions.
Your speaker is mounted to the baffle with four or more screws or nuts. The speaker has to be fastened with an even pressure around it. If a fastener loosens the speaker can vibrate and cause a buzz.
When tightening the screw or nut, you apply a certain amount of twisting force, this is called torque. You want the pressure around the mounted speaker to be even. This is done by tightening the fastener in an X or star pattern as outlined here
. It is important to not over tighten the speaker fasteners. You can damage the speaker by warping the frame.
As I mentioned above, there are many things that can cause a buzz in a speaker cabinet. These are only two of them.