The headphone output into the mixer seems a likely candidate for problems. Putting a headphone output into a line-level input raises red flags in any case, but there is surely some kind of looping going on if you're monitoing with the headphones AND feeding the headphone signal back into the mixer.

Anyway, without a more complete description of the setup (monitor speakers? what's the combo amp under the mixing board table? etc.), it's hard to diagnose your reverb/"there's a clothes dryer beside my microphone"/echo effect. I mean, it could be someone accidentally engaging the reverb effect on that mixer (Alesis MultiMix 8USB, right?)--but probably not.

Here's how I solve the problem of playing back pre-recorded clips in the studio. (Background: I am a musician, a grad student in your department, who records every day in my home studio and also does podcasts). I record in Apple GarageBand, an application better for artists than its expensive cousin Logic Express and certainly better than Audacity. I drag my audio clips into garageband a minute before I'm about to play them--then I fade their channel up as needed to bring the clip into sync with the podcast. All audio is monitored on studio monitor speakers, not headphones, and the levels are kept low enough so that the mics don't pick up the monitors and create endless feedback.

For informational purposes: my whole setup consists of four microphones run through tube preamps, a Behringer mixer, Gibson & Fender guitars + a nondescript MIDI keyboard for in-podcast live music, drum machines, and a lot of other stuff. It all goes into my Power Mac G5 via a FireWire/IEEE-1394/iLink/whatever name you'd like audio interface that gives me multiple realtime recording channels.

The point: I avoid echo/reverb/feedback by using monitor speakers wired to the mixer's headphone output and not running anything from the computer back into the mixer. I solve the audio clip problem by using multiple tracks in GarageBand (Logic Express works too, but it's less artist-friendly [or podcaster-friendly] than GarageBand).

I'm not sure whether this information is helpful or confusing. But the basic ideas are: use GarageBand (free on new macs, $49 or something for all of iLife if you don't have it), use monitor speakers instead of headphones, and don't plug the headphone out into a line-level input.

Good luck with future podcasts. I've enjoyed the first two.
    -W, musician, grad student, sound recording geek

Thanks, this is helpful. One issue is that I have been bringing my old powerbook from home to get us running, but we only have access to a CCI laptop for the long terms setup we develop--the echo-filled recording was done on that.

I did notice that some of the effect were turned up on the board and in a test when I turned them off, things got a lot better. I will look into getting some studio monitors.

Garageband is great, but I'm having some trouble imagining how you would play tracks in it while recording other tracks. Is the fading in and adding tracks something you do post-production, or can you time it so channels come on when you want while recording? If that makes sense. Thanks for the tips. Drop by sometime to check out what we're trying to set up.