Credit to barnacles10 and lithid-cm
*NOTE: Anything in brackets is either description of what is happening or an action you need to perform; don't type in anything in brackets*
What you need to do to get a boot sound on CM7/AOSP is the following.
1. http://dl.dropbox.com/u/19699565/bootsnd.sh Apparently some people had issues with the first link, so I uploaded it again. Download that file, place on your sdcard.
2. Take whatever sound you want and rename it to: android_audio.mp3 [needs to be mp3 format] and then place in your adb tools folder.
3. On your phone, open terminal emulator, and type in the following:
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 / know how to use adb, using root explorer and placing the android_audio.mp3 in the system/media folder works just as well. Reboot, and enjoy your boot sound.
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.
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:
ls [will list files, you should see 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. Enjoy.