Mine did the same thing when I first got it. I would turn it on and it was silent. I did something to the phone and had to completely restore it. After that, it worked. :shrugs shoulders:
There is a thread around here that showed me how to get the original" droid" sound as a notification ringtone. And its pretty easy to do and root isn't required. I'll look for it and post a link here
the "Drooiiddd" sound should be a sound file in the system. if you want it at startup, you have to have the original bootanimation (or one that calls for the sound) installed in data/local and the droid.ogg file in your (i believe) system/media folder. either way, the droid.ogg file should be in your system/media/audio/notifications folder.