Check the float switch on the motor oil tank, sometimes they can separate from the float causing the alarm, this is the most often cause. If that checks out then check the height of oil in oil tank on the motor. Sometimes I have had to fill the tank again to keep the float high enough to keep the alarm from going off. Check to see if there is a hole in the lines from your reserve tank. A pin hole will cause the tank to drop a little at a time.
Also that alarm can indicate water in the fuel water filter.
A solid beep is that the motor is overheating.
This is for a 2 stroke Mecury and I believe Yamaha is similar.