It's very easy to take that cover off, just use a credit card to pry it open, then unclip the sensor wire, and have a look, some cars have foam where 2 screws tighten in, that is supposed to stop the rattle.
What I did was buy some double sided tape circles, and put them around the base, almost 'jamming' the cover on when it was back in place.
Has worked a bit, not perfect, but until a better solution comes up it will do!