Vista 32 sleep mode + 8800 GTX = beep! (HELP?)

Hi,
Yesterday I decided to start doing my part 'reducing my carbon footprint' by setting up sleep mode to be activated in Vista after 1/2 an hour of my PC not being used.
Although I may be saving power, alas when my PC goes to sleep my 8800 GTX emits a loud beep.

I also understand that when Vista enters sleep mode it powers things down including gfx.
However, I gather that my 8800 is beeping because it is not getting enough power.

But, surely the clever chaps at Nvidia/Microsoft thought about this issue when designing their gfx cards/writing the sleep function into Vista?

Is there some fix or workaround available or am I bound to keep my carbon footprint as is in this regard and avoid using the sleep function.

I've searched on google and their a number of other people who have experienced the same problem. As far as I can tell no one has offered a solution as yet.