My Epic makes this random noise/chirp throughout the day and night

My phone does the same thing.  It seems it does it if it temporarily drops the 3g connection, the last time I noticed that the 3g icon on the notification bar was gone. Its also wierd it oly happens in a certain spot at home and only once in a while.  I hope this helps

3G signals are not very consistent outside of metro areas. I searched a lot trying to find a way to turn 3G off unless i want to use it, to try to save battery an stop the chirping. I am in a rural area, and have very poor, spotty 3g coverage. I now use Juice defender. It seems to extend the battery life, and it keeps the 3G turned off most of the time, enables it for a minute once every 15 minutes ( or however you want to set it) for synching . It does not seem to interfere with data connection when you want to use an app that needs access. The chirp noise when coverage drops seems to be disabled. I have not heard it since i started using it.