Droid 4 puts itself into silent mode

For the past couple weeks my Droid 4 has been switching itself into silent mode at night. At first I thought it was me, but it's not. At around 11pm I plug it in and set it on the table. At this point it is not in silent mode. In the morning it is in silent mode, which means the alarm has not gone off. After I take it off silent mode, the alarm volume is still at zero, so I have to adjust that too. And like I said, this have been the case for a couple weeks. I have installed no new apps. There are no smart actions set. Any ideas? Thanks.