the last 2 times i have been out, i have gotten the single beep warning from my engine. when i check water pressure, it is low for the rpm but quickly increases and no further warning beep. after i come off plane and fish a little, when leaving i get the single beep again. again, it only occurs once and then stops once i have gotten up to speed. water pressure again starts low but quickly comes up. any idea what gives or if there is a problem? at idle speed the water is flowing quite generously.