has anyone's ipod sounded off with a little jingle? midi like? i assumed it was off and it just played a few notes and the backlight came on... even if you leave it on, i thought it shutdown automatically. could it be a warning sound or something? there is over 3/4 battery life remaining. i've had it for a year and a half and this is the first time i've hear it. btw, i think its a 4th gen, 20gig w/ photo w/ color screen.