Why does your car shake under the seat?

A car may shake under the seat due to several reasons, including unbalanced tires, worn-out suspension components, or issues with the drivetrain. If the tires are unevenly worn or improperly balanced, vibrations can be transmitted through the vehicle. Additionally, worn bushings or shocks in the suspension can lead to instability, causing shaking. It's important to have the vehicle inspected by a professional to identify and address the underlying issue.