In the past couple days, an issue reported in the Google Web Search Help forums sparked up.
In short, it seems that some of those who upgraded their Android devices no longer can set their Google Now Reminder alerts to anything but silent.
The users are saying that they configure in settings that Google Now Reminders ring and not vibrate but they go back to vibrate and do not ring. They go to Google Now > Settings > Now Cards > Ringtone but each time they set it, and then go back to check, it goes back to silent mode.
Google's A.J. said he has escalated the issue and will report back with more details when he hears back. AJ wrote:
Thanks everyone for reporting this! I've reported this to the team, and I'll provide any updates or additional troubleshooting steps when I have any. Thanks for your patience as we look into it.
Forum discussion at Google Web Search Help.