I drive my xj down the road.....it runs great. When I turn it off.......it makes a weird humming noise from the engine compartment......also have a hard time keeping coolant in it......no leaks just had the radiator replaced......what the hell?

 

Do you have coolant getting into your oil? How long since rad was replaced? Are you sure the system was completly filled? No coolant around the water pump?

Could the hum be the E-fan?