My 2010 Mercury Mariner makes a rattling sound when accelerating quickly, for example when I'm coming off a ramp into the highway. The noise seems to be coming from under the rear passenger side. The sound goes away once i release the accelerator. Best way to explain the noise as if they were coins in a can and you were shaking it. xLarry
My car has 85000 miles.
My car has an automatic transmission.
The noise you are hearing is most commonly known as pinging or pre-ignition. This can be causes by the mass air flow sensor running the engine lean or if you do not have a flex fuel vehicle then running a E85 will cause the pinging. I recommend having the computer tested to see if the mass air sensor is indicating the correct barometric pressure before engine is started. You can disconnect the MAF sensor and road test to see if pinging goes away. If it does then replace MAF sensor and clear codes.