I usually put things like this in the News section, but nobody ever looks there.I’ll probably move it over there eventually, if I remember.
For a few years now, Harman (JBL, etc.) has been using a group of listeners to test their speakers. Part of their program is to get a set of trained listeners, and they’ve been using a software program in their training sessions for that purpose. They’ve recently released a free do-it-yourself version (Mac or Windows) which is available for download. I haven’t had much of a chance to play with it yet, but it looks like it would be good for sharpening your listening skills, identifying noises, distortion, frequency response errors, and such.
You can read about Harman’s listener training program here.
Download the program and user guide from this web page. Note that you’ll have to provide your own files for the musical examples (Harman understandably didn’t want to pay the royalties for including published material) but there are links on the download page for iTunes downloads and CD purchase of a few of their recommendations, or use some music that’s well recorded and that you’re familiar with.