[Vermont Lt]

I would imagine it’s similar to the noise that comes from a pot or boiling syrup. You hear a very light “plup” when the gas escapes. Obviously, in the 2 quart pan on my stove the sound is minimal. But there is a physical explanation. The surrounding liquid is displaced, and when the gas escapes into the air, the surrounding liquid rushes back to fill in the hole.

Now imagine that thousands of times larger. The sound would be loud and sharp.

[Sicon]

"The surrounding liquid is displaced, and when the gas escapes into the air, the surrounding liquid rushes back to fill in the hole."

That seems plausible. Would have been a good one for the Myth Busters to do. I imagine they would replicate the bubble breaking the surface at a small scale, then do the math on the acoustic effects to determine how it would sound if it was a very large bubble.