Loud popping sound from speakers

I have a Rotel setup (RB-1080, RC-1070, RCD-1072) with a pair of Definitive Technology speakers. Has been working fine for a while and now when I turn on the Power Amp there is a very loud popping sound from the speakers. Any thoughts on why this is happening all of a sudden? Could this possibly be a blown fuse in the amp? Any help would be appreciated.

Thanks.