I have a 1998 540I Sport Automatic that I have not driven for close to 2 years. It has been stored in my garage and was in mint condition. I put fresh gas in it, primed the engine and took it out for a Doctors appointment I had. Of course the battery was dead and I replaced it with a new BMW one. When I got home from the trip, I noticed a loud knock or more like a rapping or tapping noise comming from under the car. It is not very noticeable inside the vehicle, but outside it is loud. It appears to be in sync with the engine revolutions and comming from the engine oil pan or torque converter/trans. I live in Maryland. Does anyone have any idea what the problem is and if there is any qualified mechanics that could diagnose/fix the problem in my area? I bought the vehicle from Russel BMW in Catonsville, MD.

Thank you very much.