2.2, if I'm remembering right, is the first version that officially has startup and shutdown sounds available. How were you acheving it before? Were you using a the notification for mounting the SD card?
Also, if you don't have an app/widget that lets you individually control alarm, notfication, media, ringtone and system volumes, do so. Maybe you have one turned down and the sounds are there. I like the free Audio Manager widget.