Well I touched up the solder joints, and replaced the BB op-amps, at $5/ea. Now another channel is scratchy! But it happens all the time now, and I found the culprit. It's the little EMI filters right before the analog connector. I can't find the exact part, but I think these should work:
http://search.digikey.com/us/en/products/MEM2012P10R0/445-3362-1-ND/1473648