eliminate soft scraping sound behind driver's dash when hitting bumps

I picked up a TRD OR DCSB last week, and I'm enjoying it with one exception. There is a styrofoam type noise/scrape somewhere behind the driver's dash when hitting any bumps. I was looking under there and flexing the wiring harnesses, which are quite stiff and seem to make a similar noise, but I'm not convinced that's it. I can drown it out quite easily with the radio on, but I'd like to eliminate it if possible. I'll make an inquiry at the dealer down the road, but until then does anyone have pointers on what to look for or where it's coming from? The truck doesnt yet have 100 miles on it.