Why does my MacBook Air (13-inch, Mid 2013) randomly beep at me?

Macbook Air

OS X Yosemite

Version 10.10.3

1.7 GHz Intel Core i7

8 GB 1600 MHz DDR3

My MacBook Air keeps randomly beeping at me. The began yesterday. I turned off the speaker so I could continue to work, but this won't solve the problem, obviously. Today, I've look online hoping to find a solution. I get information that's dated several years ago. One suggestion is to turn all the sound notifications off, but when done and leaving only the necessary sounds on, I still get the submarine-like sound. The notifications left on sound differently than the random beep I get. Sometimes, the beeps occur in bursts of three or so then quiet for a while then just a beep followed by random beeping periodically. I cannot discern any pattern. Even when the screen is asleep, the random beeps occur.

What distresses me most is that I keep finding others who've had the same problem (within Apple's support system) but with no answer. Is there anyone out there who can help?