I have a knocking sound when my car is cold. I switch to syntec blend oil this time. I know I have enough oil. I used the right viscosity, 5w-30. Does anyone think I should switch back and do another oil change? It only happens if my car has been sitting for a while and then the sound goes away after I drive down the street. Its as if the oil isnt being circulated as soon as I start the car. Could this synthetic blend be my problem?