Passenger Seat Rattling

Good morning, all,

my '13 GLS has recently developed a rattle in the passenger seat. I know that's what it is, because if someone is sitting in the seat, or I press against the seatback, the rattle stops.

I'm sure this is being magnified by the absolutely horrible roads left behind by the "winter wonderland" we've had, but I'm not sure I can continue to drive 46 miles twice a day without thinking about running the car into a telephone pole.

Short of a trip to the dealer, can anyone direct me to the most expeditious way to resolve this?

Thanks!