Unknown, Random sound - I would like to find the source so I can disable it.

I have a Verizon Samsung Galaxy Nexus,
Android 4.1.1
Kernel version 3.0.31-g396c4df
build number JRO03O

A few weeks ago, my phone started making a sound at random intervals. I would call it a notification, but there aren't any notifications that align with the sound.

I added an app called Notification History, followed it's instructions, but it never logs anything, even for actual notification bar notifications. It is a two note sound, the second note higher than the first

How can I determine the source of this sound so I can turn it off?

I would go through your ringers and see if it is a ringtone or notification tone.... If it's not then it is some sort of system notification.... How often does it do it? Did you install any new apps around the time it started happening? Do you have LiteFlow installed? I have heard a lot of people reporting odd behavior like this.... What do you use for for voicemail? Is it some sort of reminder for a missed call or message that just hasn't been cleared?

I figured out it was Yahoo! Mail app notifications. I had to re-install the app around Christmas and I disabled notification bar notifications, but I didn't disable notification sound.