ga-x48t-dq6 / PC Speaker makes fluttering sound and/or a quick beep

I just built a new machine, including the ga-x48t-dq6 as the mobo. Some of the key specs are listed below. After I'm logged into windows, the PC speaker will randomly do a quick "flutter" sound. The amount of time the fluttering lasts is about the same duration of one normal PC speaker beep. Sometimes it sounds like a very quick beep, lasting for half the duration of a normal beep.

I should stress there have been no crashes, no blue screens, no freezing. I can't reproduce this on the fly. As for frequency, it seems to happen no more than once every 1-2 hours. So far I haven't done too much with this PC other than surf the web. I haven't done anything beyond that. That includes no gaming.

1. What would you suggest as next steps for me to diagnose the root cause?
2. What would be the cause of something like this?
3. Bad pc speaker?
4. Bad motherboard?
5. Something else?

If you need any additional info please ask. My return/exchange window with newegg expires in a little over 2 weeks, and I'd rather deal with them than the vendor.

Thank you!

--- Specs ---
CPU: Q9450
Memory: CORSAIR XMS3 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Dual Channel Kit Desktop Memory Model TW3X4G1333C9DHX
Motherboard: ga-x48t-dq6
Video: 2 diamond ATI Radeon 3870's
OS: Vista 64
Power Supply: Rosewill (Newegg's brand) 750W and plugged into a new surge protector

--Bios settings--
CPU Fan Fail Warning - DISABLED
Smart Fan - ENABLED

Not overclocked.