Why is there a rattling noise coming from the back of my car?

I have a 2012 honda accord it has 28k miles on it and lately when i drive on uneven roads or go into potholes the back of the car where the speaker are rattles a lot very loudly and it's annoying. Always the side of the passenger seat rattles. Any ideas on why this can be before i take it to the dealer to check it out?

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