Southbridge controls SATA / PATA interactions with the CPU. Perhaps your recent "tinkering" has caused the issue to re-appear?
I'm 99% sure that the MCH voltage had nothing to do with this. This is my fourth board, my first with Gigabyte (which has this control, unlike Asus), and they all exhibited this behavior, even prior to any tinkering.
I'm really getting to the point of thinking it is an issue with my copies of vista. All 3 copies were from the MSDN download sections (I have a subscription), so at this point I can only assume it is that.
the hardware, including drives, work fine with XP.....this only shows up in vista, so I can only think it is a Vista issue. I'm gonna see if I can buy a copy of Vista Home Premium retail and see what happens.