My case has been escalated a couple of times and the current word from "engineering" is that the system is operating as designed. They claim that the beeping happens when Nvidia Optimus switches from the onboard graphics controller to the Nvidia card. I told them that I didn't buy that answer. The whole point of Optimus is that it handles the change while remaining transparent to the user. Why on earth would they (Nvidia, Dell, etc.) make the switch produce a loud beep that you can't disable? This led me to play with the Optimus settings and I never could produce a beep on demand. So I downloaded the "Optimus State Viewer." I can see when the video card changes from integrated to the Nvidia card (when opening Google Earth or other programs I have set manually) and there is no beep. However, the beep still occurs randomly, even when I'm not sitting in front of the computer.
Dell has been very good about contacting me and keeping me informed of the progress on my case, but I don't buy that Optimus is producing the beep by design at all.