I've had my Nexus 5 for a couple months, and all of a sudden within the last day or two it plays a chime every time I unlock my screen, which is VERY annoying. I can't for the life of me figure out what is causing this. I checked my sound settings, and the screen lock sound option is disabled. I also went through all of my running apps to stop the processes, and it doesn't seem to be any of those. It's also not my normal notification sound, it's a different sound I'd never heard before. It's driving me crazy. Any ideas about what it could be or suggestions for troubleshooting this? Thanks!