weird gray line on control panel windows

I have an XPS 14 laptop running Windows 7 Home Premium.

I've had several hardware issues, and recently had the motherboard replaced. Diagnostics run after the replacement were all normal, and the machine seems to now be running fine.

However today, out of the blue, when I launch Control Panel, I see an odd grayish line (maybe 2-3 centimeters thick) across the left-hand side of the window. The main control panel window looks normal (whether I do category or icon view), but when I make a selection (like Network and Internet, or Hardware and Sound, or System and Security) and the appropriate window comes up, there is a gray line/bar across the left-hand portion of the window (the blue-colored section where the list of options to select is found). It seems to be located about halfway down from the top of the Control Panel window.

To be honest, as far as I can tell there is no effect on the functionality of my machine or my ability to use Control Panel, and so far I haven't seen anything like this with any other programs or windows, so I should probably just ignore it.  But it's very weird, and it's not normal.  Also, this computer is less than 3 months old, so I feel that I shouldn't be dealing with such issues.

Anyway, has anyone else seen anything like this, or does anyone have any suggestions as to a cause?