I have a Whisper and an Aquaclear filter that has done this. You need to clean the motor. It gets gunk build up and will not turn the impeller efficiently. Unplug the filter, take out media, turn the filter upside down over the tank to empty, grab the motor and twist clockwise and pull. It will come off. Take a q tip and clean the inside of the motor. Make sure to clean the groove in the motor housing. Rinse it well to make sure all the gunk is out. Then put a little Vaseline on the rubber seal. Be careful when putting the motor back on because the rubber seal ring can pinch and cause to not seal properly. It may take a few times to get it seated right. It is a good idea to add a little water to the filter before re installing it to make sure you do not have a leak. Then put everything back together and prime with treated water. It should start right up. If there is air trapped in the impeller housing just raise the impeller shaft up and down a few times and it will get rid of it.