Gigabyte GA-MA78GPM-DS2H Long Beep during XP loading

[OldGrowthSalmon]

POST is fine (just the one short beep as normal)
Loads XP Media Center Edition fine
But when CPU is overclocked, I get one long beep during XP booting (not POST).
I lower CPU to "Auto" speed in bios, and no more beep.
Ran memtest to 70% and it read zero errors.
Googled and found nothing here or elsewhere. Only hits are for beep codes - which I think are just for POST?
Also, once it beeped with two long beeps -- But just the once.
No red flags under event viewer. No problems that I noticed using xp. No other errors that I found.

Ga-ma78gpm-ds2h
Phenom X3 710 Processor (Toliman
latest (f5) bios
antec earthwatts 380
mushkin 996533 800 mhz 2GB pair running unganged
Windows XP MCE version 2002 Service Pack 3
currently running at 2.99 GHz
CPUID says system clock running at 115 and 15% overclock, with a multiplier of 26

As always, any help is much appreciated. Thanks to LSDme for much help in the past w/ this board!!

[wazza300]

it could be your psu isnt powerfull enough and its beeping because of low cpu voltage? also make sure you disable floppy boot device if you dont have a floppy drive installed

[OldGrowthSalmon]

boot order is:
First: HDD
Second: Disabled
Third: Disabled

FDD is disabled (and not present)
I thought maybe the "no-fan alarm" was sounding, but I still get the beep after disabling the no cpu fan alarm and the no system fan alarm. It definately turns off and on depending on whether I set the CPU to overclocked or not. I can't figure it out. It's weird.