sounds like its time to take the pump apart at the very least and inspect it. vibration? water flow to motor blocked? pump QUIT? almost sounds like you (they) sucked a plastic bag or some rope, or something. first thing would be to look up through the intake (bottom of boat) with a flashlight and see if there is any debrit. take the hand hole cover (top of the pump) off and inspect through there aswell if possible. some hulls dont allow you to see through there very easy. remove any debrit and try it. if you dont find anything, it will need to be taken apart and inspected. removing the bowl is fairly easy if you are somewhat mechanical and have decent tools. if your not very knowledgeable with pumps id suggest taking it to someone who is. rebuild kits are roughly $450 for the kit with new impeller. labor prices vary.