On my 97 E320, the bottom mount of the radiator assembly is less than static, so a good bump on the bottom, like when parking, can push it back and has made the fan make contact before. It also caused the aux fan motor to rub the top of the front bumper. How I fixed it, sort of, is to just pull the bottom of the radiator back into place forward whenever that happens. I also put the aux fan assembly back on its bolts at the top (it attaches to the radiator) and shoved a tennis ball in there to keep tension on it.