Continuous buzzer usually means something is properly wrong. It;'seasy enough to top up the oil, but I would guess if the oil level dropped to empty it swould shut itself down. My old yam was premix, but my Auto mixing Suzi gave a good few mins of intermittent buzzing when the level dropped to "warning" levels.
So, assuming it's your thermostat, there appear to be 2, one at the top of each cyl head. If it's your water pump it's down at the bottom of the leg, accessed by removing the grearbox. (and before you start hammering the cav. plate to get it out there is usually a bolt hidden under that trim tab anode at the trailing edge)
If you have no tell - tale "pee", it's likely your pump or a blockage. if you have reduced Pee it may be one of your thermostats is jammed shut, so overheating one side & tripping the overheat alarm.