This morning I made my coffee as usual - I used a Capresso machine, poured it into a clean cup, added 2 packets of splenda, and a bit of half and half. About a minute or 2 later I noticed a buzzing/fizzing sort of sound coming from my coffee but how could that be? I put my ear next to the cup and lo and behold it WAS coming from my coffee!!!
Why was my coffee making noise?!
Dammit why is this thread in GQ?? 
Anyway my first guess would be superheater water and splenda. Your coffee is essentially “boiling” around the splenda.
The reason why this is a guess and not a “for sure” is because you’re not microwaving the water, you used a Capresso. I’m not sure what kind of machine that is, but it looks like a Nespresso kinda thing, and I don’t think you could possibly superheat water in those.
Don’t drink the bees
Superheater water, I like it 
Tabby_Cat of course meant superheated water, in case there was any confusion.
I suspect:
Your cup has a crack or imperfection in the glaze and the heat of the coffee is causing the air within the porous material of the ceramic to expand and be blown out of the crack, making a noise as it goes.
If this happens below the surface of the liquid, it will make a little stream of bubbles, ending in a small patch of bubbly foam on the surface of the coffee.
OH SNAP!
I know what’s causing your sound now.
Your table had some water on it. The base of your cup has a continous raised circular ridge (as is common in most mugs). When you set your cup down, the continuous raised ridge and water trapped some air under it. This air was then heated by the cup and expanded, and thus “bubbled” out from under the cup.
This sounds vaguely like a baby making spittle sounds.
Happens to me all the time!
but really, don’t drink the bees
I’ve heard fizzing noises coming from a coffee cup before, and it was from a crack in it on the inside forcing air out.
i’ve had cracks or voids discharge air and do that.
Buzzing sound?? That’s a mean load of caffine you’ve got there.
Was it a double walled, insulated cup? If so a small leak will evidence itself by the hissing of expanding air/bubbling of water and air from the last time it was washed as the inner liner heats up, and heats the air between the two sections.
The water wouldn’t be boiling - it doesn’t boil in the machine, let alone 5 minutes after brewing + adding cold half and half
I don’t see or feel any crack or imperfection, and there was no patch of bubbly foam on the surface
Nope. The sound continued even when the cup was off the table.
Why would the water boil around the splenda - wouldn’t the splenda just be absorbed into the water?
FWIW, my wife did not put splenda in her coffee and her cup didn’t buzz at all.
If the noise continues when the cup was off the table, then I still think mine is the right explanation - maybe the hole in the glaze is very small and is somewhere near the top rim of the cup, above the fill level.
I want what he’s having.
I’m new on here and am surprised that a noise coming from a cup of coffee can have so many comments. So, I couldn’t resist, I had to comment too on the hissing coffee cup. I’m gonna go with the crack in the cup.
I’ve had the experience of cleaning baby formula bottles with nice hot water, then placing them upside down on a metal sink surface to dry, and having the sound of the resulting escaping air audible from the other side of the apartment. My money’s on escaping air from a crack or something in the mug, seeing as how the noise continued after the mug was lifted. It doesn’t have to be visible or tangible to make some noise.
Anyway to tell for sure?
Weevils in your beans.
My coffee was making a ticking sound for about 10 minutes after I poured the cup I didn’t notice the sound until after I drank a third of it (straight black). And then just below half it stopped. I have been drinking coffee since childhood never encountered this before, at first i thought it was the computer but definitely the coffee mug. No holes, no chips, and no cracks. Am I alone?