I previously posted about a strange sound noticed when starting or stopping. well, i finally found it. not sure how the item got in the car, i suspect an assembly line worker put it in there as it is in a spot where it could not get in from the interior floor. so, if you hear something rolling around, check under the passenger seat.
A marble? That old chestnut! Have you upset the dealer (or tyre fitter etc) or messed them about at all? Now I'm not saying they dropped the marble in as it could have arrived there in many, many ways, but it's also one sure way of pissing off a customer who's messed somebody about. Just saying.
Actually that marble is functional. It was preventing spiders and other critters from taking up residence in that space. Warranty voided!
See the caution notes on "Spherical vitreous inclinometer removal" in the factory manual, under Auditory Hallucinations. Requires ecu reset with Techstream.
I think it's all part of Toyota's experimental IPAS system, or "Internal Proximity Alert System". The Moveable Auditory Reverberation Ballistic Loudness Element or MARBLE is designed to provide sight impaired people with auditory warning clues that they are riding in a Prius.