Ahhh, that is the sensor package, the M1131 is a fire support vehicle, that box is what does it.

I don't usually quote Wikipedia, but they pretty much have it:

"The FSV provides enhanced surveillance, target acquisition, target identification, target designation, and communications supporting the SBCT with ”first round“ fire-for-effect capability. It integrates the current M707 Striker Mission Equipment Package. The FSV provides the Fire Support Teams (FIST) with the capability to automate command and control functions, to perform fire support planning, directing, controlling and cross-functional area coordination, and execution."