Tan band across photos at high ISO settings?

I've been testing out a new camera, and I just now realized that at a high ISO setting I get this tan line, which is sometimes in the middle, sometimes on an edge, and sometimes not there at all. I've never seen this happen before. What might the cause be?

Using a Nikon D600, tested with two different lenses with the same effect.

the line:

It looks like part of the image is being lit by incandescent and the other by daylight coming through a window.

Try again with All the light being supplied by one light source and with the cameras white balance set to that light souce

No idea. Check with Nikon.