Maybe Greg can help me here:

I was asked by a colleague to help him xfer an older existing Pro Tools session into his Radar system, so he could mix it for a client (he doesn't own Pro Tools).

The session was only 14 tracks (jazz), so we connected the AES/ebu outputs of two 888's to go digitally directly into the radar. Everything was clocked with my Lucid Genx6.

To our consternation, we were getting loud digital pops, seemingly at random. Sounded a lot like a clocking problem, but further inspection showed they were occuring on the existing specific tracks at specific times. Nothing appeared to be out of the ordinary looking at the wave-forms in the edit window, but I increased the horizontal resolution click by click on the original tracks, until "magically" a perfect rectangular shape appeared. Two audible clicks would occur in this region: when the cursor first hit the front border of the "box", and then again as it passed by the back border. Increasing horizontal resolution to sample level showed that the box (which might be a few seconds in total duration) was actually a series of perfectly shaped triangle Wavesspaced extremely close together! The Waveswere inaudible, except at the onset and outset of the region. This seems to imply they are at a frequency beyond human hearing.

Additional note: the triangle Waveshad either a completely positive or negative "polarity" (if that's the correct word?). That is, in any particular region, the waveforms extended from the center baseline only up or down, not both.

My question is, what would produce such a phenomenon? I didn't think DC offset would look like that, but could it be something related? Each time the box-like shape of triangle Wavesoccurs, it is apparently at random and unrelated to the musical activity of the track. It tended to occur mostly on the same three or four tracks (Left piano mic, rack tom mic, room mic). If it had been on just one particular track, I might guessed it might be a manifestation of a short circuit somewhere, but on multiple tracks that seems less likely.

Fortunately, they are only two or three per song, often on non-critical tracks, so the music may be salvageable with some judicious editing. But I'm still wondering if anyone had ever seen anything like this before. I know I haven't.