The plastic will be from the first day he got it. Look on the driver door, it has a blue piece of something to protect it from being banged into stuff.
Hussein, your questions seemed very troll like, as did some of your replies (hence why I made my comment & I will stand by that).
depends what you mean by vibrating,do you mean against the floor or just vibrating by themselves,if its the latter the rubbers holding them up may have been broken when you had the work done on your cats