It is normal for the voltage on a car to drop when you start the engine. The starter motor is the one thing that consumes the most electricity in the whole car.

The battery icon appearing during car-start is normal and I would not worry about it unless there were other problems.

Currently, my amplifiers pop when I start the car while the player is playing music, and I'd like to get to the bottom of that one. But the battery icon appearing is normal.