[Obsidian Dragon]

I have an AMD Sempron 2600+ running at 1.6 gig.

This is not related to your problem with the high pitch tone but in case you did not know, the AMD Sempron is not supported with Protools and in the past it has been the cause of a lot of problems for people trying to use it anyways.

As for the high pitch tone, what digidesign hardware are you using? Some users of the original Mbox, Mbox2, Mbox 2 Mini interfaces have reported similar issues with the USB interface or USB cable (I have not heard of this problem with the Mbox 2 Micro yet). Try a different USB cable first and then perhaps a different USB port on the computer. Some have needed to get another USB card for their computer because the existing one had improper shielding. If you are using a digi001, 002, 002R, Mbox 2 Pro, 003, 003R, you might need to try swapping the firewire cable and then card. Also make sure your power cables and monitor cables do not run near and parallel to you audio cables. Watch where you place your power brick for any device.