The first rock to activate is directly behind the spawn. Just keep running into the back corner where you will see 2 stone columns fallen. The meteor is nested between them.
The second meteor rock to unlock the zombies song is near a small brick wall on the perk side of the bridge.
The third and final rock is downstairs from the main circular room. Follow the railing to the sand bags and it is sat on the floor.
Listen, and enjoy.
