first thing to try is replace cmos battery with a brand new one and clear cmos settings by reset RTCRST jumper on motherboard.
My Optiplex 760, with all drives removed, makes 6 buzzes, not beeps, from the black piezo device soldered to the mainboard 1/2 inch from the heatsink's port side. It was able to boot into Linux Debian Stretch last week, but then repeatedly switched off, following the boot message line: 'clocksource switched to clocksource tsc'. Thanks for your help.
Optiplex 760 buzzing alarm