It could be several things. Most commonly is a motor mount known as a "Dog Bone". It allows the engine to kick back and forth making noise.
Open the hood of the vehicle and have a helper change the gears from D to R. Watch the engine to see if it is moving excessively. Also, with the helper's foot on the brake, have them press the gas lightly while it is in both D and R. If the engine raises more than an inch, chances are you have a bad motor mount.
Let me know what you find.
Joe
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Tuesday, November 24th, 2009 AT 11:10 PM