My first thought is use an audio program with a feature that elimates those pesky noises by muting the Hz/pitch signal/channel.
Funny you mentioned this, I was looking at "
Ray Gun" last night which does something like it (though I think it specializes in simple tape hiss rather than mechanical hiss). I haven't used the program yet, so I can't recommend it. I will say that I did go looking for VST plug-ins for "Audio Hijack Pro" which has been a great asset to me. If you're using a Mac, might want to check out these links:
http://www.pure-mac.com/audio.html for possible solutions.