My 8 year old 308 has just started developing a knocking sound coming from below. It seems nothing to do with the steering as it happens in a straight line. As the road deteriorates, the noise starts with each bump and increases as the bumps increment, until it almost sounds like popcorn popping in a pan on some roads . You can also feel the vibrations from the kncking. The car is well looked after and only has 60,000 miles on the clock. Cards on the table, what could it be and what would it cost to fix? Suspension? Engine mount? Axle?

Thanks for your time.