Yes, you can disable it, but you have to update your bios to do so.
Go to epox.com, get the bios dated 12/10 (only one there for the 8rda+), install it, then go into 'Integrated Peripherals' in the bios. There will be an option called 'AC97 at Post'. Change that to 'Disabled' and the system beep will go through the system speaker (if you have one attached to the mobo) instead of the sound card.