Is this considered clipping in marine boat stereo help!!!!

Yes I just recently bought a new clarion marine head unit to replace my existing stock stereo in my boat. I replaced all 4 existing stock speakers with new Polk audio speakers. After wiring the head unit, everything is fine and operational except when I turn the stereo up it does not distort as normally would if the speakers were not getting enuff power from the stereo. Well I turn it up and it makes this noise like it's clipping or as if a cd was skipping here and there but it's not the cd tried a couple as well as the fm radio does the same thing but only when the stereo is turned up. I got ahold of the people I purchased the unit from by email and he said to try and ground it differently. Now i'm not sure why this would cause it to clip cuz I just used the same stock ground wire that was going to my old stereo...please help

Thank You,