A rod bearing doesn't always knock from the moment you turn your car on it could knock wright when you turn it on at a high rpm or even like 3500 rpms not all bearings go out the exact same way and vito a valve is gonna make a knock noise crazy If your hearing a knock noise stop driving your car because your gonna cause a problem that cant be fixed like through a rod out your block my friend just did the other night it wasn't nothing nice but his happened within 15 min the motor started knocking 15 min later he was covering up a big ass oil spill in the middle of the road