The knock they refer to is usually experienced under a load when accelerating. However, I could be wrong. The fact that you don't hear it under the hood indicates it's most likely not the engine. It could be something between the trans and engine, torque converter, loose flywheel.
Regardless, I recommend you have it listened to by a mechanic. See what they say.
Wednesday, December 17th, 2008 AT 9:21 PM