i have a knocking noise that has increased in volume over the past few weeks. Under the vehicle, it seems to be above the oil pan. The oil is full and clear and has been changed every 4,000 miles. It uses no oil at all between changes. Has anyone had similar issues with a 2001 RX3000 AWD? My thought it could be a rod bearing. When I put it in reverse, it may go away momentarily but return. That makes me think it is not a rod bearing. Any thoughts?