2003 Ford Expedition If not U joints, tires, or wheel beari

Noises problem
2003 Ford Expedition V8 Four Wheel Drive Automatic 98K miles

After 1 of my coils went, then replaced, pedal vibration was evident, especially louder after 72. Gets worse when releasing the pedal below 70. Showing signs its getting worse. Steering wheel does not vibrate. So I can assume that the front end is just fine since the tires where replaced (thought it was the tires) and inspection was done showing no front end problems, everything is tight. Ujoints where replaced less then a year ago. I am hearing a slight clicking noise when starting from 0, very very weak noise, thou I Do hear it. When switching to 4x4(switch), I hear a low clanking noise from transfer case, not to loud thou, but louder then normal. If not Ujoints, tires, bearings, or any other front end parts, could this be something in the front transfer case, like maybe (hopefully) just low diffential fluid?