If your car sounds like there are rocks rolling around somewhere in the car, chances are that your exhaust pipe may be a little loose.
The best way to check is to safely slide under your car and shake a few things around until you find the culprit. Make sure the car has cooled off before doing so; you don’t want to burn yourself.
Lift the car off of the ground using a jack and slide under the car. Find the exhaust pipe about 60cm behind the engine. Look to where the seats would sit, there will be a slim metal cover between the exhaust and the floor of the car – rattle this around gently to hear for the sound of the exhaust rattle.
If you find that the cover that is loose, tighten the bolts from underneath the car.
If the shield has been bent, don’t fret, you can bend it back with pliers or a screwdriver. Make sure that whilst fixing that noisy rattle, you don’t hit the very sensitive oxygen sensor.