Well, I think I might agree with slitterst about the cause of the background noise on my new recording setup. I think it's my mixer (a Behringer Euroback UB802) causing RF interference.

Here are some sample MP3s:

• Nice mic and mixer, raw (1.7MB, ~2 min): a straight recording, no post-processing
• Nice mic and mixer, processed (1.7MB, ~2 min): post-processed with noise removal, compression, and normalization. Listen to this if you want to hear me sound like a robot in a tunnel.
• Nice mic and mixer, processed (1.7MB, ~2 min): post-processed with compression and normalization (no noise removal)
• Cheap lapel mic, no mixer, raw (404kb, ~30 sec): Lapel mic plugged straight into the computer, no post-processing
• Cheap lapel mic, no mixer, post-processed (404kb, ~30 sec): Lapel mic plugged straight into the computer, post-processed with compression and normalization (no noise removal). This is what my podcast normally sounds like.

I also made a recording of my cheap lapel mic going through the mixer, but it had the same background noise as the nice mic had, and you could hardly hear my voice. I didn't feel like trying to get the levels right since it was obvious that it was having the same problem.

Another thing that made me think that the mixer is the problem is that the first time I tried to record with the cheap lapel mic going straight into the computer, I was getting the same interference. As soon as I unplugged the mixer, the interference went away. That's pretty damning evidence right there.

Well, I guess I'll still see about trying to make a recording with my new set-up in a more remote location again, just in case there still is a chance that I can make a decent recording with my new set-up, but I'm very pessimistic about the whole issue at this point, so I'll also be looking into how to return/replace the mixer.

The really disappointing thing about this whole situation is that I bought the UB802 on the recommendation of several other podcasters -- it's often described as "the podcaster's best friend" -- and also because it is specifically advertised as having a high resistance to RFI. *sigh* Maybe I just have a dud mixer and a replacement will take care of it. *crosses fingers*

And if I don't go with a straight-up replacement Behringer, I'm open to any suggestions for a replacement pre-amp, prefferably with the mixing capabilities that my Behringer has. And, yeah, in about the same price range.

[Update: More information: it's probably not the mixer.]