91non Turbo KNOCKING SOUND PLEASE HELP
 

Have recently noticed a knocking sound on a 91 Stock 300zx non turbo. 120K miles. Doesn't sound like a rod and its actually sounds near the top of the motor. When I first herd it I thought it was the fan hitting the shroud. No performance difference at all. I drove the car from California to Chicago and it ran fine. What could this be, any suggestions. Would like some info before I tear it apart.