Update. My R-4 has sat with Edirol tech support for 4 days now. I called to check on status since I was told it would only take a day or two to turn it around. In talking with support, they indicated they could not duplicate the problem. I asked them how, exactly, they were testing. The said 4 channels of 24/96. Okay, never mind I reported the problem occurred when running 24/48. And in what format, I asked. 2 x stereo.
The support rep, Chris, indicated I must be using it in a vibration-heavy environment.
I
specifically stated at least half a dozen times in previous calls that the problem
only occurs when running 4 x mono, and that it occurs in a zero-vibration environment (my home office, recording dead air). From here on out, I speak only with Ted at support, since he's the only one with whom I've spoken to actually comprehend the problem. (Anyone out there experiencing tech problems, I recommend doing the same - I think there are only 2 of 'em in the R-4 tech support group.)
Frustrating...