Electrical Ground Loop Interference Herringbone?

[ChrisNicols]

I have a new mysterious issue to submit. I have noticed these drifting diagonal lines all across the image on a small number of u-matic tapes now. The description for 'Electrical Ground Loop Interference Herringbone' fits it, but it doesn't look like the image example provided on the article.

That article states the Herringbone issue usually stems from a wiring problem. Since its only happened on a few tapes, I was going to chalk it up to being baked in when the tapes were originally made. However... this artifact doesn't show up on my two CRT monitors, only on the computer monitor while its digitizing and on the resulting video. I have done over a hundred u-matic tapes on this set up, but I've only seen a handful of them with this issue. Is it possibly something else entirely?