Need Help With "Buzzing" Sub

I have a 7 year old Monitor Audio Silver RSW-12 sub that has been working great until recently.  I moved the sub, carefully, to have the carpets in the room cleaned and now all the sub will do is emit a loud buzzing noise.  It does this with/without the input connected.  I took it apart but dont see anything obvious like loose connections, burnt wires or circuit boards, etc.  Any ideas?  Can this be fixed?  Are replcement amps even available for this unit?  

Thanks,
Chuck