well, the wheels on the car go round and round, when the meat hit's the skillet, it makes a sound.
amount of juice on coil, in wick, being vaped at given time, will cause different sounds, but sizzle is usually a friendly, I'm working kind of sound. And all gear will give off different sounds and noises, depending on type, style, material used, watts vape at, air flow, juice ratio, everything effects everything in vape land.
All these things should make one wonder why, and investigate, strike a theory, and experiment. Leads to a better understanding on what makes vape possible, which leads to one being able to improve their vape. It's like seeing bubbles in the tank, tells you it's wicking properly, and gurgles tells one, a wicking/flooding issue is involved.
Being able to listen to what ones vape is saying and tasting you, also leads to better understanding and vape.