Hi,
I started getting random beeps once, it turned out to be my motherboards CPU overheat warning - I'd been set far too low. As tempuratures rose that summer my PC ran a little warmer. I just changed the setting to something more realistic.
I've had the same happen when one of my fans connected to the motherboard failed and I got beeping to say a fan was running below its minimum. Oh, I also got the same once when I fitted some silent low-rpm fans that spun below the motherboards minimum acceptable level - I had to disable fan monitoring all together to get rid of that.
Might be worth checking settings in the BIOS to see if any such warning beep was set.
Note: My beeping started with the odd beep, then got more frequent.
These were all on older motherboards, not on my new Sandy B.
I guess it's worth just double checking all settings in case it's something as simple for you as it was for me.
Cheers,
Scoob.