Agree, its most likely the mud. In the front it can get caked into the rotors and any voids in the back of the wheels pretty good. If its still there after a good cleaning, check that you didnt knock off any wheel weights. If you aired down and did much bouncing to get over stuff, couldve spun a tire on the rim, too.
2013 JKUR - AEV 3.5" RS, Metalcloak front control arms, PR44, TW FDS, Synergy Suspension high steer, drag link, track bar, steering stabilizer, etc.
spieg's build thread