iPod Touch - Static Noise

I have an iPod Touch 2nd Gen. The software hasn't been updated in a while too.

Whenever I push the lock/power button and it makes the click (any screen but the lock screen), there is a very faint static noise that follows it for a few seconds. It's so faint that you can't even hear it without putting the speaker up to your ear, and that's at full volume.

I assume this always happens, but I've yet to notice it. My question though is this a normal thing or what?