Try tightening all the screws and bolts you can get to from the outside first. Check the port to be sure there isn't something in there.
Unless you see something from the outside it is going to need to be taken apart. Something has come loose inside (amp? bracing?) or the speaker is coming apart or rubbing.
Unless you see something from the outside it is going to need to be taken apart. Something has come loose inside (amp? bracing?) or the speaker is coming apart or rubbing.