Mine was doing the same thing. Felt like it was on the left side, and could feel it in the floor when I turned.
What it turned out to be was where the track bar mounts to the axle, the hole was ovaled out, and the track bar was popping around.
Eventually, the bolt wobbled around enough to work the nut off, and the bolt fell out while going down the highway. WORST death wobble EVER! No track bar @55mph = not good.
I had a grade8 washer welded to the mounting bracket to repair the ovaled hole, put an adjustable track bar on, and it hasn't popped since.