After going through three pairs of Apple's in-ear headphones (replaced by AppleCare) I finally decided to find out why they were going bad. All of my in-ear headphones would eventually lose most or all sound in one or both earbuds, somewhat suddenly. I took them apart to find that the speaker itself was still nice and loud; the culprit was a small amount of wax embedded in the fine mesh in the cap of the earbud. Disgusting, I know, but I kept the headphones extremely clean and they still became clogged. I've read about many people having this same problem on other forums, so here's how I fixed it.

• Pull off the silicone ear piece
• Using a pin or a tiny screwdriver, pry off the metal ring against the back part of the earbud
• Using the same small, sharp instrument, CAREFULLY pry the end cap off by inserting the pin into the seam that is revealed after removing that metal ring
• Take the endcap that you just pried off (the piece with the metal mesh in it) and take it to a sink
• Close the drain stopper in your sink so you don't accidentally lose the little endcap
• Flush it out with hot water and blow through the open end of the earbud (the end without the mesh) to clear the mesh
• Repeat until screen looks clear
• Reassemble earbuds. They should just snap back together and stay that way without any glue. Use a little glue if it's not sticking, but be careful not to get any on the speaker or in the mesh screen (naturally).

Notes: You don't have to blow through it using your mouth. That's what I did, because I don't have any compressed air, which might be a better solution since I can't comment on the potential toxicity of the dried glue left on the open end of that endcap. I did this and haven't died, so, uh, Q.E.D. Also, you might as well do both earbuds at the same time here. Even if one seems OK here, it's almost definitely got some amount of blockage that you can clear.

So there you have it! You've saved yourself a phone call if you have AppleCare, and $40 if you don't. It's amazing how such a tiny amount of junk can block almost all the sound from those speakers.