Hi robchi. Welcome to the forum. The 2.7L is known for oil-related problems in the engine if the oil is not changed at the recommended intervals, but this sounds more typical of an exhaust leak. You might be able to replicate the sound by holding the brakes while trying to accelerate in gear. The leak will be in front of the catalytic converters, usually right where the exhaust manifolds bolt to the engine. It might not occur until the engine is warmed up.
If you are unsure, have a mechanic listen to the sound to give you a more definite diagnosis.
Caradiodoc
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Wednesday, May 26th, 2010 AT 5:59 PM