Hi,
More than likely, it is your phone's signal fluccuating between a 3G data signal and 1x. It is trying to lock into a good data signal and will use a lot of power searching for a signal. My suggestion would be to first, dial *228 and use option 2 to update your PRL. Then, make sure you are running the latest sofware OS for your device, 5.0.0.732 which is available for download at http://vzw.smithmicro.com/blackberry/ You can check your OS version on your BlackBerry by going to Options>About.
Doc