These bars work well on our car. They are almost (but not quite) silent. We did not purchase a dam for this, and it would seem -- not necessary. One issue with the "world" (read: "wordless") instructions: the bars are designed with channels on both upper and lower surface, presumably for installing certain Yakima-brand accessories, and two rubber strips cover the channels, and by design, the installer cuts pieces off of these to both shorten and gain outside pieces that slide under both edges of the mounts, providing a nice clean factory look. The issue is, with basic installation, the top rubber strip does NOT/NOT need to be removed, and the instructions aren't clear. In the event, I removed both strips, and created extra work for myself putting back the upper strip (by far the more difficult one to handle between the two).
2011 BMW 3 Series 4dr