Did you install the drivers off the disk when you installed W7 64, or direct from the Gigabyte site.
Just dug out the manual for the board, go to page 44, look at PCI IRQ Assignment, try disabling them if you don't use them see what happens.
Also if you don't use serial port,parallel port, then disable them, see page 41
Set your PCI Express Frequency to 101 might stop default back to auto.
Did you install the drivers off the disk when you installed W7 64, or direct from the Gigabyte site.