Could be "spark knock" which is the premature detonation of the fuel in the cylinder often caused by excessive temperatures in the cylinder (engine running hotter than normal), ignition timing advanced too much (this is computer controlled so its not likely the problem), poor quality fuel, etc.
Have you noticed the temperature gauge when this is happening?
Are you using the same type fuel as before (when it didn't rattle)?
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Monday, August 4th, 2014 AT 4:13 PM