I have the same issue. I set the alarm for 3.10 at night and I never hear the alarm. No I do not have my am/pm mixed up. My clock is set on 24hours. Where did you find the "alarm even in silent mode" option?
BTW. I'm rooted with the xFuZiiOnZz rom.
Mountain Dew makes me happy.
If I've helped you, a thank you would be cool.