My friend has a 2008 V6 with the shaker system. A few days ago his battery was dead and he assumed it was just because it was old and replaced it. Now a few days later the new battery is dead also. He noticed that while the car is completely shut off every few minutes you hear a loud pop through the speakers as if the amp is cutting on and off. Is this a common problem with the Shaker system? What's going on here?