My 2002 150 EFI has, for years, intermittently sounded the steady warning buzzer when coming up on a plan after idling. It does it maybe one in ten times. Now the buzzer is occasionally coming on when simply at idle. If I just bring boat back down to idle when in hole shot and start up again, buzzer goes off. If at idle, I usually go to neutral or turn key off and back on. Have replaced water pump and thermostats. My mechanic is clueless. Any suggestions?