I have only heard it once while on road... it was after going through the dip into my driveway while moving faster than normal.

While offroading the bang is only when you have a quick drop off. If you are moving quickly and come to a ledge/hole/or rolling over rocks where the front end is "bouncing" up and the front end fully extends.

There are 2 ways to fix this. The first is as mentioned by the TC Upper Control Arm which redefines the location of the arm. The second is to grind the areas that are in contact with the bucket. This can be done because that portion of the UCA is excess steel as it is only a lip.

My personal opinion is that there is no structural damage being caused (just cosmetic paint), its mostly a sound discomfort. My overall goal with my X (which is 1 year old in my possesion today) is to put the 5" lift on. If I were going to be done with the spacer lift right now I would not have a problem removing the steel that is in contact with the lower bucket.

See this pix for extend of banging area.