Bubble Water sounds

I've had this sound on my MacBook pro play for over a year and haven't been able to find the origin. Can't remember exactly when it started but I've had this computer for over 3 years now and wasn't a problem at first. I kind of ignored it for a while until I've had to present slides onto a TV and speakers and the sound has played extremely loud even when my laptop is on mute. There's no notification that pops up, I don't use any 3rd party apps that were on at the time of the sound playing, and I've checked the activity monitor for anything unusual. Nothing. I can find nothing and it's driving me nuts. Any suggestions would be great.

Sound traits;

• Doesn't matter the instance, date, or time; it plays
• Is not associated with anything visual pop ups
• Always plays extremely loud no matter what my volume is set to
• Plays on headphones, computer speakers, or any other audio output I'm connected to when the sound plays
• Sounds like water bubbling
• Hasn't changed at all since it started