OK, follow up on this, Matt's post from the SD board below:
This is very strange. I listened to the mp3 files, and to my ears, sounds like a problem with the A/D converter chip. If it were a problem with the analog circuitry preceding the A/D, the level would change along with the gain pots. I very much doubt that this is a firmware issue. As unlikely as it sounds, it does seem to me that both of these cases are A/D converter problems. Please contact our support guys - Jon or Justin and we can arrange to get the units back to troubleshoot, or we can send you a new A/D board, which is a fairly straightforward replacement.
Matt
I just got off the phone with Jon and he is going to send me the AD board immediately...said it is a simple swap. Will report back...