It hasn't gone off since, and has been on all day today. Will have a look at Gigabyte's support.
EDIT: It just happened again. Oddly enough, when it occurs everything works fine while it is beeping (music, mouse cursor, internet, everything) except my keyboard, which was new yesterday. When I hit ctrl+alt on the keyboard, it stops. I did this last time in the process of hitting ctrl alt del, and the beeping stopped, and tried it again just now and it worked. It also happened both times while I was typing. This is weird!!! Any ideas?