Black marks on back of cab

I've had my '12 tacoma since new, 4 months of ownership. I've only hand washed it twice but noticed from the first wash about a month in that I had a mark on the back of the cab, directly across from the trim on the top of the bed.

Washed it again a week ago and noticed that I actually have one on each side, in the same place. I may be able to buff them out but they don't respond to anything I can do by hand.

It would almost appear as if my bed has slapped against the back of the cab. I've never driven with the truck fully loaded, nor driven recklessly across potholes or rough terrain, could this have occurred during installation? Anyone else with these scuffs? I'll try to get some pictures in the morning. Kinda sucks, the truck is white and they're the only things I can't improve upon during a detail.