If you’d like to have a different sound played automatically every time you start your machine, you’ll want to run a brief script on startup that chooses a random sound or song from a given directory, then play it using either the built-in Sounds preferences panel or by specifying the path to your favorite audio player.
This tip assumes that your sound files are stored in /boot/home/config/sounds — edit to suit if you store them elsewhere.
Add the following to /boot/home/config/boot/UserBootscript:

N=`date +%S`
N=`expr $N + 0`
I=0
for file in /boot/home/config/sounds/*; do
	I=$[$I + 1]
done
N=$[($I * $N) / 60]
for file in /boot/home/config/sounds/* ; do
	if [ $N -eq 0 ]
		then
		rm /boot/home/config/settings/Sound
		ln -s "$file" /boot/home/config/settings/ Sound
		break
	fi
	if [ $N -ne 0 ]
		then
		N=$[$N - 1]
	fi
done

Now, copy one of your sound files to /boot/home/config/settings and rename it „Sound.“ If you want the sound to be played via the operating system’s built-in startup sound function, launch the Sounds preferences panel, select Startup in the main panel, and choose Other… from the picklist. Navigate to /boot/home/config/settings/Sound.
Alternatively, you can simply point SoundPlay, MediaPlayer, or any other audio player at your Sound link from ~/config/boot/UserBootscript. For example:

MediaPlayer /boot/home/config/settings/Sound & 

Make sure the audio format of the sounds you choose are supported by the player you use.
The idea and 99% of code for this script was taken from the tip Shuffle your background Images by Jason Scaroni.