Sounds like something i need to look into. Video source may be hard to find though
The /system/bin/bootanimation file has to be replaced. Back up your old one; just rename it .bak since it's so small, then reboot and the sound should work.
edit: I think I renamed mine .nosnd or .orig or similar. This is a one time thing (though may need to be redone after any kind of rom install) and it shouldnt hurt to leave it in place indefinitely