G35 loss power on acceleration/knocking noise from engine

my 2003 G35 had a knock senser code and also loss power on throttle and a noise comes and goes from rear end of engine. i repair replace the sencer and also repaired the wire to sencer it had been chew by a rat. then after test drove the car and the power came back then i came to a stop and noice came back from the rear end of the engine,but no dtc found and the car loss power ...any idea help. sorry for spelling