jw; It may well be that, but let me ask a few questions. Is it more obvious when cold? Does the sound change with an increase / decrease in RPM? Can you hear it at idle with the hood up? If you can hear this noise while it is parked and running you should be able to home in on it by grabbing a piece of tubing / length of old hose and put on end to your ear and the other near areas of interest. Make sure to avoid the serpentine belt. You should be able to isolate it if it is happening at idle. Get someone else to rev the engine while your listening. If it is not happening while the car is not moving that also helps rule in or out possible sources. Be careful and let us know what you discover.