Yes, the plastic cover can be easily replaced, however it is a whole piece with the surrounding plastic - check page 9 here: http://www.toyota-tech.eu/aimuploads/d93d0ea5-24b0-4cc5-b78c-8a781d09d6d2/Toyota_C_HR_Foot_well_illumination_LHD_PW527_10003_AIM_004_063_0.pdf
As for the rattle, I had something similar from the passenger door which turned out to be the seat belt clip. Check the belt if it touches or if it is near any of the plastic covers.
As for the rattle, I had something similar from the passenger door which turned out to be the seat belt clip. Check the belt if it touches or if it is near any of the plastic covers.