dumb question, but something I have always wondered what the fuck it was. I noticed on all BMW's, on the rear bumper, there is always a small square plug w/ radius corners maybe the size of a half dollar or so (but not round, its sqaure) it looks like just a simple pop in plug for maybe where a bolt goes, but come on, no manufacturer in there right mond would just put a ramdom bolt/plug over and over and on different models. Personally it bothers me and I see it as an overall eyesore (call me weird0. I was thinking maybe a back up sensor. Oh yeah, it is always on the passenger side of the rear bumper maybe 1/3 the distance from center. anyone????