I had this problem with the alarm on my Droid Bionic not too low of a volume, not being loud enough.
I first checked the media volume, which I learned, does not control it. Then I checked the details on the alarm, and couldn't find anything on volume, other than increasing volume as it sounds. I made sure to clear this.
Then I backed up a screen, to just the alarms, for all the alarms. I found the menu, clicked on Settings, and THERE finally found alarm volume. I have adjusted that setting, and things are working well now.
I hope this helps anyone struggling with a low volume / not loud enough alarm on their Droid Bionic.