Help with speakers

I am having a problem with what i think is my speakers cutting out. I have a 1997 Nautique super sport and the sound system is Clarion (well atleast the head unit). Whenever I try and turn the volume up above about 28-29 the whole thing will turn off and then turn back on until I turn the volume down. I was looking at the options and when i TURN THE bASS TO -7 AND THE treb to -7 they can go to about 30. Also, when i CHANNEL THE SOUND TO ONE SPEAKER OR THE OTHER IT CAN ALSO GO TO ABOUT 30 BUT THE SECOND i TURN THE BASS OR TREBLE UP, OR HAVE ALL 4 SPEAKERS PLAYING, IT ONLY LETS ME GO TO 28. Please help.