GarageBand and the bizarre problem with garbled/distorted sound

Hello all,

We are using GarageBand to record our (surprisingly popular) podcast, but we've been experiencing a MASSIVE problem since just about day one. My apologies for the long read, but I'd rather cover all of the bases in one go.

The setup:

- iMac 3.6 GHz, 4 GB RAM, OSX Lion (10.7.3)

- RME FireFace 400 (kernel driver v3.06)

- GarageBand '11

- Four microphones

As we record the podcast, GarageBand will sometimes sort of "snap" without warning and lower the pitch of one recorded channel for about a second (an effect we like to call "the testicular drop"). The voice of whoever is talking briefly drops several octaves, and this is preceded by a visible "snap" in the actual audio file (which is NOT visible in the real-time recording view, nor is the octave drop audible). This, however, isn't nearly the worst of it.

Sometimes this drop is followed by GarageBand starting to produce garbled, distorted sound from one recorded channel which then "bleeds" over every other channel, i.e. the entire four-channel recording. We won't hear this during recording (so we never know when it's going to strike), but the corruption is found in the recorded tracks during post-production.

The sound corruption completely destroys the sound from all channels and huge chunks of audio become completely unusable. The buzzing lasts anywhere from a matter of seconds to several minutes, then sort of "fades" ever so slowly away (think of a huge distortion plug-in slowly fading off). Rebooting seems to have no effect. The corruption comes and goes as it pleases.

We record over four mono channels, but my audio interface (RME FireFace 400) does all the heavy lifting, so it shouldn't be a performance issue. The problem also persists regardless of whether we catch the conversation over 4 mono channels or 2 stereo channels. The strangest thing is that the problem seems to occur mostly after we've had a break in recording (I stop the recording, save the GB session, we have a brief break and resume), so the first half of our podcasts are usually very clean of drops and buzzes, but often minutes upon minutes of the latter half have to be cut. However, this oddity does eliminate the possibility of it being a latency issue.

We use four Shure microphones connected to the FireFace 400, which is connected to my iMac via FireWire. We use dynamic microphones, so the problem can't be connected to phantom power. No other devices have a hand in the recording process and I can't imagine this being a problem with the FF400, so I assume it's something with either GarageBand or OSX.

We have tried pretty much everything from stripping the channels clean of plug-ins, experimenting with different preamps and mixers, changing every cable to switching input/output configurations, but the problem persists. Interestingly enough, the problem occured both on Leopard and now on Lion, as well as on different GarageBand version iterations (I recently upgraded from Leopard's "in-box" GarageBand to GB '11, to no avail).

There is one strange bit of insight that came to light during our last recording session - this was by far the worst noise attack during our podcast's relatively brief history, whereas the previous recording session went nearly without a hitch. The random nature of these occurences leads me to believe it something that happens in the background, like, well... Time Machine? It's just about the only thing I HAVEN'T tried switching off during recording.

If any of you have suggestions or experience with problems like this, please let me know.