Since installing Raidroid 1.1 I had the concern of an extremely LOUD boot sound.
I decided to find out how to turn it off and let everybody know how.
It turned out to be much simpler than I thought. The method, I believe, will work with all ROMs.
There is a file in /system/media/bootscreen called boot_animation.xml - this contains the script that runs on startup.
First you need to copy that file off your phone for editing. Use any method you wish, I used adb
adb pull /system/media/bootscreen/boot_animation.xml boot_animation.xml
Now, in your current folder, you will have a copy of that file. You can edit it in notepad.
Here is mine:
You will see, I've highlighted the changes I made in bold.
I've disabled the audio completely but I could, for example, change the image or audio to anything I wanted. If you choose to change the image or sound file, be careful. This script runs at startup and I'm guessing that if you configure it wrongly that you may not be able to boot the phone.
Once your phone is edited, you now need to upload the amended file back to the phone. Again, I used adb. (thanks DarthOps for the remount help)
adb push boot_animation.xml /system/media/bootscreen/boot_animation.xml
All done, now reboot your phone to test.