Taken from somewhere here in xda. (
http://forum.xda-developers.com/showthread.php?t=1048231)
I cleared cache and dalvic using CWM.
I flashed a fresh CM7 nightly using CWM.
I Followed terminal emulator instructions...I'm sure adb from command line will work also. I used root explorer to copy android_audio.mp3 (don't forget to set system folder as R/W with root explorer.
1) search for and Download the bootsnd.sh file. Save it to the root directory of your SD Card on your Device.
2. Take whatever sound you want and rename it to: android_audio.mp3 (needs to be mp3 format) and then place in your adb directory.
3. On your phone, open terminal emulator, and type in the following:
su [enter]
cd /sdcard [enter]
ls (to list all files, you should see bootsnd.sh)
sh bootsnd.sh [enter]
You won't see a confirmation, or message, it just runs, and returns you to a # sign.
From your computer, adb push the android_audio.mp3 to the /system/media folder, reboot, and you'll have a sound.
If you don't like or know how to use adb, using root explorer and placing the android_audio.mp3 in the system/media folder works just as well (Mount the /system as R/W First). Reboot, and enjoy your boot sound.
*NOTE*
If you flash / change roms, you'll have to re-run the process to enable the boot sound again. If you get tired of it / don't want it, you can use root explorer and delete the file.
Alternate method:
For those that don't like using the terminal emulator, you can do it via adb:
navigate to your adb folder via commanda prompt, then issue the following commands:
adb remount
adb shell
cd /sdcard
ls [will list files, you should see bootsnd.sh]
sh bootsnd.sh
Like in the emulator, you will be returned with a # sign. Then place the audio file in the folder I specified. Just decided like posting an alt method
Sent from my LG-P999 using XDA App