I built my brother a PC about a week ago, and ran into one issue along the way. I didn't think to post this, because I got it working just fine, but I just remembered, and thought I'd run my experience by the community. This involves an 8800 GT EVGA.
So we get the system all hooked together, it boots up just fine, installs the OS, everything is jim dandy. However, when we went to put the case back on, I had to rearrange some wires. In the process, I needed to take out the video card. When I put it back in, I forgot to install the six pin that runs from the GPU to the PSU (it was about four in the AM at this point). When I went to power it back on, the computer uttered this spine tingling scream.... literally, the computer was howling like a banshee. So I turn it off and go to power it back on...remembering to plug in the power this time...it POSTs and boots, but no picture.
I'm crapping myself at this point, so I put in an old 7900 GT I had laying around: boot and video. So I think, maybe, I could have fried the 8800. But I take out the 7900 GT, put back the 8800 GT (making sure to plug in the bloody power) and the thing boots right up, with video. As of this moment, the card is running per specs, and producing wonderful frame rates in all the latest games (ie: it's working perfectly, and has been for over a week).
My curiosity lies in the scream the computer made, and the fact that when I replugged it in the first time, it didn't produce any video. Any ideas? Maybe the bit of power it got from the PCI slot scrambled the memory for a second, and the power had to drain for it to reset itself? Maybe the computer was possessed for a moment?
Actually, I remember back in the day when I tried hoocking up on my PC an old 230W PSU from an old Dell when my 450W PSU was fried. It didn't even post but there was this electrical whine, but not as lood as you say. I wouldn't worry if I were you. This has to do with oscilations in capacitors and other components (such as transformers) which couldn't get the power needed for normal performance, so they made this sound.
That board of mine is still working after 5 years of torture so don't worry about it.
Anyhow, the scream more than likely came from the power supply stuggling to pump enough juice to the 8800GT and the rest of the motherboard over the PCI-E line. I've heard pretty hair-raising stuff come from PSU's in the past. Count yourself lucky your PSU didn't blow a capacitor or kill itself.
The GPU issue highlights one of those things that i love about being a system builder. You can be met with nothing but a dark screen, that sickening feeling of failure and anguish about seemingly frying some expensive and exciting piece of kit, but somehow, most of the time, things turn out fine.
Your theory sounds alright to me ( both invalid memory and the poltergiest), but it strikes me as a bit uncomforting that current GPU's wont even boot without the extra juice. I remember doing the same thing with a couple of systems running 5900XT's back in the day when additional power connectors were becoming mainstream. They booted fine, installed fine and were even completely stable. Only noticed when i tried running FarCry on them and was met with a slideshow.
I know that particular scream very well. For those that have never heard it, it's not something you'll ever forget to your dying day!
I believe it's just an audio alarm warning you that the graphics card is not receiving the amount of power it requires (had the same thing happen when I forgot to plug in my new X800XL a while back).
As for why, after you did connect power and restart the system, you got no image, I can only guess as it didn't happen to me. I did, however, after the initial scream and subsequent shutdown, remove the card from it's PCI-E slot and reseat it before powering up the system again.
If you listen closely, you will notice that the scream comes from the video card, not the system speaker or the PSU.
It happened to me once when I was reworking the innards (eVGA 680i mobo and 640 MB 8800GTS). I forgot to reconnect the 6 pin power connector. Turned the PC off, plugged the connector in, and the system camr right back up.
Yeah, it shouldnt have caused any problems when that happened, as long as it was powered down when you plugged in the power. At some point with my last 3 cards I have powered the system up without plugging in the external power, 2 Nvidia and 1 ATI card, and they all did that same thing.
When I took the stock cooler off of my 8800gt I did notice a small round thingy on the pcb and thought to myself this looks like a small speaker but I wondered why they would out a speaker on a video card. Now I know but I wish never to hear it go off !