@erik_squires Good point on the power supplies. I have a LPS on the streamer and the far end FMC. No guarantee that the LPS is not creating noise as well, but is probably better than the supplied SMPS's.
I have concluded, unscientifically, that the issue is the Cat 8 shield connecting the devices on both ends via the metal jacketed plug, and introducing noise that messes with my router, FMC's and ultimately my streamer. I don't think there is anything wrong with these cables, they are functioning as designed, but the connected equipment is not able to deal with it.
@rbstehno That said, maybe I will pursue some finer Cat 6 cables if they exist.
Keeping the fiber, as it is a great upgrade, just swapping out to Cat 6. If you have a little grunge on your upper end, I think it is worth a try and see if this cleans it up.