I've got a 2014 PiP and have an annoying rattle - it sounds like plastic on plastic, coming from the interior rear seat or trunk area. I can't find anything obviously loose, has anyone heard/fixed a problem with their Prius? If so, what was causing the rattle?
I found some large pliers and other various junk underneath the rear seat base, from previous owners and or inattentive mechanics. It just pulls out so worth checking. I find the rear spoiler can rattle on cold days too, or something around the tailgate. It's fine when it's warmer.
Not to rattle you any further, these sounds will trick you into swearing they're in one place when they throw their sound from an unrelated location. I suggest you begin by emptying both glove boxes, the center console storage, door pockets and anywhere else you laid anything down. I'm betting the sound will clear up at that point.
