Drive Train Axles Bearings problem
1998 Ford Explorer V8 All Wheel Drive Automatic 166000 miles

Just recently I notice a noise comming from the front it only sounds when I let go of the gas and the car is slowing down from 35 to stop. it kinda sound like if I were in first gear. but Im not. I just bougt the truck last year. I wonder if I have to change the gear oil in the axels or ? the tranny is good and clean and works fine. I would appreciate any help thank you. Also my check engin light is on. I took it to auto zone and they gave me the code (po133 ) where is that located and how difficult is to change. thanks again