The easter egg seems to just trigger code in other modules in the car to do their part with proper timings. Audio is handled by the CID (MCU), and if it's bogged down by anything that could lag it enough to delay audio starting after engaging the rest of the modules then it will not be in sync since the process doesn't seem to be synchronized in any way besides start time.
So, my suggested steps to those experiencing sync or other issues with the show:
- Ensure your car is on firmware 2.50.114 or higher. Any lower versions will not work at all or not work correctly.
- Park in an open area with nothing overhead, and nothing around the car that can be picked up by any of the ultrasonic sensors.
- Reboot the 17" screen with the scroll wheels and give it a few minutes to get everything back together and start fresh.
- Stop any music that is playing. If using bluetooth audio, set the media player to something else then stop to make sure it doesn't auto play something from your other device.
- Set your apps on the 17" screen to ones that use basically no CPU, like the energy window and calendar and turn off HVAC. Even if you have one low-intensity all full screen, I've noticed that the car doesn't actually unload the previous half-screen app in all instances.
- Close all doors except the driver door.
- Input the modelxmas code.
- After the window pops up on the screen, crank the volume if desired. Do not dismiss the popup.
- Exit the car.
- Manually close the driver door (physically push it closed, not with the fob or handle).
- Walk away from the car so as to be fully out of range of the ultrasonics.
- Single tap the top center of the key fob.
- Enjoy the show.
I've done the show probably 30 times now, mostly without issue. It is pretty picky about things that are picked up by the ultrasonics and abruptly stops if something is too close. Had someone approach the car to get a close video and it cancelled the show.
Good luck!