I had this problem on the front passenger side. It looks like the carpet is a little small or has shrunk. I fixed mine by adding a piece of leftover home carpeting under the carpet. I cut a piece to match the contour of the floor area and put it under there. This was thick carpet I used, carpet pad would be good too. Anyway it gave enough of a rise that the factory carpet would tuck nicely and hasn't come out since. I don't notice any other difference from this either. My kind of fix (cheap and quick).
