G251 Power LEDs flickering

What I'm working with is a Taig CNC with 3 G251 drivers, a C10 parallel board, and a KL-600-48 PSU.

I've recorded a video (below) showing the issue I'm trying to track down.

The power is flickering to the G251 drivers intermittently. I guess what puzzles me most is that this only happens some of the time. Yesterday I ran the mill through a whole project for a few hours without an issue, but often the machine won't go for ten minutes without the power flickering. Even in the video you can see that the power will hold for a few seconds before it goes back to flickering.

I don't suspect that it is an issue with the G251's themselves, but rather something with either my wiring or the power supply.
When the G251's are flickering, the PSU voltage is also well down from the 48V it should be. That said, if I remove the load from the power supply, it doesn't exhibit any issues.
When the power is working like it should, I can operate the mill as expected and the steppers work just fine.

http://youtu.be/RM88Vf_0tec

I'd appreciate any suggestions on possible causes or troubleshooting tips.

Thanks!