VisorCentral.com (http://discussion.visorcentral.com/vcforum/index.php)
- How To / Troubleshooting (http://discussion.visorcentral.com/vcforum/forumdisplay.php?forumid=2)
-- Backlit Buzzing (http://discussion.visorcentral.com/vcforum/showthread.php?threadid=2494)

I just received my GVDx a couple of days ago. Last night I noticed that when it is in backlit mode, there is a faint, audible buzz/hum that I can hear about 2-3 inches from my ear. When I go to normal display it goes away, except for a really, really faint buzz if I put it right to my ear. Do all Visors make this sound?

Yep,
I don't know where, but it's been discussed here. Everyone has it.

This isn't unique to the Visor, either. My Pilot 1000 and PalmPilot Personal did that whenever I did anything graphics-intensive or (with the Personal) used the backlight. You may also hear it briefly when changing apps. I think it's something in the display circuitry. Harmless, part of the thing working, but odd if you aren't used to it.
Some early electronic calculators (especially with LED displays) squealed pretty good if you filled the display with 8's!

The high-pitched squeal is a characteristic of all Indiglo-style lights. If you happen to have a cheap Timex digital watch with Indiglo, turn the light on and hold it up to your ear -- you'll hear the same sound that your Visor makes.