1995 Jaguar XJ6 Car Makes noise when accelerated

I recently purchased the Jaquar and have made 3, three hour trips on the interstate and have driven it short distances a few times around town. Upon returning home from this last out of town trip the car all the sudden makes a kind of rattling noise when accelorated. This car has been a one owner car to my knowledge and seems to have been well maintained. Yet when I purchased the car I simply went on his good will that the car was in great shape. Your advice would be greatly appreciated. Thank You.