Thank you all of you guys for answering my questions. I really appreciate it. I took my car back to mechanic this morning. He figured out that he bent a metal/rubber hose during belt replacement. Metal part of the hose was touching the car body and making vibration. He moved away the metal part from car body so that it does not touch the car body longer. However, it is still a mystery to me that how moving hose away from body fram changed the engine noise to normal. I guess maybe it was an airway or exhaust component or something, but I am happy for the result. My car is back to normal with brand new timing belt and water pump. Thank again.