If the sound is coming form the battery its because electricity is arcing (like lightning) from a metal or soder point to the battery. This in itself isn't too dangerous however eventually it make lead to the battery failing. If I where you I would visit cheapbatterypacks.com and grab a new battery right away.
Again I said this isn't "too" dangerous however there is a possible fire hazard here.
etd/Carmelo - Team North Bay
v3 Aeg specialist