So, to remove those two sounds I used silent .wav and .ogg files.
Using RootExplorer I copied:
PowerOn.wav to system/etc
Shutdown.ogg to system/media/audio/ui.
If you still like having some sounds during startup/shutdown, you could make your own files (.wav for startup and .ogg for shutdown) and copy them to the folders as above.
I have attached the silent files that I use if anybody wants to use them.
Edited by wes58, 08 August 2010 - 10:32 AM.