How to identify and remove a looping sound? I have a Nexus 4 running Android 4.4.2 (not rooted, but with developer options enabled), and it keeps developing a stuck looping sound (I guess part of a notification sound, looping approximately every second). It survives shutdown / restart, and I've been through killing processes and services, and apparently at random at some point after killing everything, it sometimes seems to stop (sometimes it keeps going no matter how many you kill)...

...but it keeps coming back. I'm at the 4th or 5th time in 24 hours where I think it is fixed, only to find it bleeping away later. Obviously this makes it hard to leave the volume on!

So: any ideas on identifying the offender? Maybe some tool that can display the sound buffers by originating process? Or just flush them...

Note: it also survives a reboot into safe mode, continuing to play in a loop while in safe mode.
Hard to say what could cause this problem. 
Maybe you're able to tell what happened before the sound started? Could be a hint to address the issue.

I would recommend start with uninstalling any unecessary apps and going through every app that is/was ever generating notifications for you. Check their internal settings (if there are any) and also check notification settings in app manager. 

If you're using developer mode I suppose you can also try to turn it off, just in case.

If it's reacting on shake in a weird way I'd also recommend to run all possible updates, alternatively reinstall apps or in the worst case: reinstall the system. Can't tell more about what could cause the bug.