This freeware voice recorder will open the usual music formats and save as WAV or MP3.
After opening the track, select the section you want to reverse, and choose Reverse from the Effects menu.
To export as MP3 you will need to locate and download lame_enc.dll (also free, do a Google search).
For audicity visit the Nonags website.
MP3 files seem to grow when saving, but since you only want short tracks that shouldn't be a problem. You can also add voice comments to the track via a microphone.