Tallrussell

I recently installed a 2.5 inch BDS front leveling kit and some larger tires. A few days later I took it in some mud on a property that I own nothing too rough maybe 5 minutes in some slightly muddy terrain. When i left i noticed a slight rattling / grinding coming from the front. It doesnt always make the noise only occasionally when im driving over 25 MPH and only in 4x2. It sounds almost like there is something loose or maybe a stick is stuck somewhere. Ive looked the truck over pretty well, taken the wheel off and looked it over and made sure everything was tight. Also when its making the noise if i shift to 4x4 it immediately stops. Its a brand new 2012 FX4 ecoboost with less than 4000 miles. I dont really want to take it into the dealership and have them tell me that the leveling kit voided the warranty. Any ideas on what it might be?