Audio System problem, is it a fuse?

I was out on Friday and all of a sudden my stereo system would do weird things when I would turn it up loud. It would play normal for a second, then it seems like the speakers would cut in and out, or the sound would rotate from one speaker to another.

I don't think the speakers are blown because all of them behave this way whether on the tower or in the boat, and they sound just fine when the volume is low.

I was wondering if someone has an educated idea if I blew a fuse, or and amp, or something else. Any info would be helpful.