I have 2 brand new Dell Optiplex 380 and 780 PCs with optional DVI boards for the Integrated Intel G41 display adapters running Windows 7 Pro (Dell OEM).
Whenever the power settings are set to put the monitor to sleep, the computer plays the "Device Disconnect" sound every 7 seconds. This only happens when using the Dell provided Intel driver and the monitor is plugged into the DVI card. The problem does not happen when using the Microsoft default video driver or if the monitor is plugged directly into the VGA analog video port.
I want to use the Intel driver, because it has the pop-up application which allows video settings to be changed including rotation of the screen image. This has been reported to Dell, but they indicate it must be a problem with Windows 7. It does not happen with Dell/Intel drivers under Windows XP-SP3.