Just a question are you using something like Easytune?? this comes with a cpu and system case temp sensor which can be alarmed with a beeping.
If so try unintalling it, unless you use it for overclocking ur system
Then you will need to find sensor and hit the H tab i think it is and then one off options on top is to activate alarm deactivate that reboot should go.
Just a noobs view took me ages to figure mine out when it was doing it.