system
Given the following post, respond as if you're commenting on Reddit:
human
Why does water start to "roar" just prior to boiling?

I've noticed that when you boil water in either a kettle or a pot, the water will start to make a low roar just prior to an actual boil, when small bubbles start to nucleate on the bottom surface of the vessel.

Is there a particular reason for this?
gpt
The bubbles that form rise into the slightly cooler water above them and quickly condense, collapsing with a 'click'. This happens many times a second with many collapsing water vapour bubbles, producing the roaring noise.