problem with some of my sounds

I have uploaded some sound effects to play with but I am having some issues. All of my sliders are turned up so that's not the problem. I cannot hear some of the sounds when I play them. Others can hear them but I can't. This isn't an issue of format because I even have 2 sounds that I edited from a longer file and they were made in the exact same way at the same time. One file will play fine and I can hear it, the other will apparantly play in world (always? sometimes?) but I can't hear it. This issue is happening with several of my files, not just the one mentioned, and seems completely random. Files that worked yesterday I can't hear today and files I couldn't hear yesterday at all are working perfectly every time today. Any ideas?