Something I have noticed in Windows 7 (and Vista, though that is hearsay, since I don't have a machine with Vista to test this on) is that it messes up your system volume for minecraft occasionally. To fix this, right click your volume meter, go to Open Volume Mixer, and then check the level it has MineCraft's volume set at. It randomly mutes mine sometimes, and I have to fix it this way. Hope it helps!
Note: You must have minecraft running to adjust its volume properties in the mixer. Not that you wouldn't have it running. Does it even have a quit command? Not that you'd use it.
Maybe this is what was intended, or maybe this is just for us Mac people, but here was my solution: (as of the newest update):
After you have downloaded and installed the sound files in their place, actually disconnect from the net to force offline mode (an empty password doesn't work), check for the sound. Once MC is up and you hear the sound, you can reconnect to the net.
Thanks theknife! It worked a treat! Used the download.
Just a tip to those who it doesn't work for:
When using the F3+S trick, hold the F3 key and hit S a few times. I had to spam my S key to get it to go. It does work eventually tho. And if that doesn't work, try holding the S key for a few seconds.