Not at all, and we have 75 mph limits. They give you 5 "cone thingees" that go behind the deflector. When I first put mine on, I tried it without them and it did rattle. Since I installed them (you know, following the instructions) there's just a barely noticeable vibration at speed but no noise at all.

 

How was the install on yours, pretty straight forward? Is there enough of a gap where you can get down behind it for washing? I assume a little flex in the plastic so you should be able to.

 

The install was very straight forward. I had one issue with the thickness of the metal on the hood, but worked that out. There is enough of a gap for washing, but it's also easy to just take the deflector off (5 screws).