I recently updated to 5.0 on my stock Nexus 4. Phone is not rooted. at least once or twice a week the phone will randomly shut down and reboot with no warning. On other occasions, the phone will lockup when using the stock messaging app (not Hangouts) and either reboot, or go to a blank homescreen with just the wallpaper and no app icons, then reboot as normal. On one occasion, I got a loud buzzing from the speaker before the phone shut off. Not really sure what is causing this.