Banding with Radeon HD 7970 and Dell U2412M

Hi all.

I just built my first system in 15 years, and I splurged a little and picked up an AMD Radeon HD 7970 paired with a Dell U2412M monitor. After installing the latest Catalyst drives from AMD's website, I'm noticing banding when I log into Windows; i.e., there is banding when the system fades to black and then back to the desktop when logging into Windows.

I'm pretty sure the monitor is not the culprit as I used this monitor previously with a Deall Latitude e6410, and I didn't notice the banding when logging into Windows; the fading to black and back to the desktop was a smooth transition there.

Does anyone have any ideas what could be causing this? I'm new to AMD GPUs, so I don't know the various Catalyst settings that could be affecting the problem.

Thanks for any direction.
MR

PS. Not sure if this matters, but my MB is an ASUS P8Z68-v Pro/Gen3, and I did not install any of the display drivers on the board; the only display driver I installed was the Catalyst. That said, my Windows Device Manager does not report that I'm missing any display drivers.
PPS. One more thing to note. I picked up a new DVI-D (Dual Link) cable for the new system -- it's 10 feet long. It's a high quality cable from Tripp-Lite. This is the first time I've used this cable, so I wanted to throw that out there. The display itself looks fine -- it's the fading-to-black where the banding shows up.