I believe that the sound is the power supply for the little video
screen on the cell phone. When the screen goes dark, the squeal stops.
When the screen lights up, the squeal starts. It does not matter if
a voice call is in progress or not.

I can hear a similar sound if I hold my old Palm PDA up to my ear.

I showed the phone to two coworkers and described the problem. Neither
one of them could hear the sound. And both of these guys are younger
than me! Ha! That's what you little punks get for listening to all
that loud music. Your ears are more jacked than those of a middle-aged
man.

Anyway, now I hesitate to take the phone back to Verizon. I doubt that
the sales staff will be able to hear the sound. They will just think
that I'm mean and crazy.