PC Waking from Sleep Mode By Itself

A couple days ago, I watched my PC wake from sleep mode by itself. Yesterday, it was already awake when I got up. This morning, I was awakened by the bright monitor turning on around 4:30 AM. I've never seen this before in the couple months since I built this PC. The most recent hardware/firmware change was upgrading BIOS from 4507 to 4752 about 2-3 weeks ago. But my PC and I had at least two weeks of uninterrupted sleep (couldn't resist the double entendre) after the BIOS update, so I'm not sure that caused it.

Wake/Sleep Settings: Basic power settings are turn off display in 20 mins., computer sleep in 30 mins., hard disks off after 45 mins. The Intel 82578 network adaptor was set to wake on magic packet. I disabled that, but I'm skeptical about something on my home network accidentally sending the correct magic packet. I also disabled Allow Wake Timers. That didn't help either. Any other ideas?

I'll post this issue on some Windows 7 sites too, but want to check BIOS/firmware first.

OS: Windows 7 Pro x64

Motherboard: Intel DP55KG

CPU: i7 860

Storage (system): Intel X25-M G2 80GB SSD x 2 (RAID-1)

Storage (data): Samsung F3 HD103SJ 1TB x 2 (RAID-1)

Video: PowerColor AX5750 1GBD5-S3DH HD 5750

BIOS version: KGIBX10J.86A.4752.2010.0217.1029

Chipset: P55, INF version 9.1.1.1022

Intel RAID Driver RST 9.5.0.1037 (10/2/2009)

Marvell 6145, BIOS 1.2.0.31, Driver 1.2.0.7103 (9/15/2009)