I have an '04 C320 wagon with a bad rattle that appears to be near the back bumper. Dealer can't find anything wrong. Spare tire has been secured. Over a bad bumpy road still sounds like loose pipe wrenches in trunk. Anybody else with this problem?

 

This still is housekeeping issue, not automotive engineering issue.

Though the dealership could not find a loose wrench floating around, there STILL IS such thing hiding there under the carpet somewhere. The best person to find it is noone but you.

Most spare tires are secured with dish-up position in a Benz. But if yours is secured mouth-down position, there could be something underneath it.

If you absolutely could not find anything, have someone drive it over a bumpy road and you stay in the back and listen. Make sure it is from the inside of the car. If so....keep on looking. If not, we have to look outside for the culprit. Pay a shop to raise your car up a lift and search for loose parts.

 

forgot to mention...the fifth door.

there could be a nut or a bolt that the factory could have left behind or simply gotten loose inside the assembly of the rear hatch door. in that case, u try your best to shake it; swing it up and down abruptly or something.

if you are lucky, you may find some gold tooth that a factory worker had lost.