This is a problem with the A4 sport package. Lots of owners bottom out on speed bumps, even when being careful. It's also possible to scrape the front valance ("spoiler" equivalent) on driveways, etc. when the angle changes. A couple of people have even reported destroyed oil pans! Audi's sport package is 20mm lower (about 3/4") lower than non-sport. From some source, I heard that the BMW sport pkg. is about 15 mm lower (a little over 1/2 inch).
Has anyone had ground clearance problems with the sport package on the 99 E46, particularly 328i? It could be that the "lowered" E46 still has significantly more clearance than the "lowered" A4.....or maybe not?