I have a 2006 Nissan Altima with a 4 cylinder. When I turn the ignition off the engine continues to make a noise like a roller bearing continues to move for about one second. All of the frive belts and accessories are stopped and the noise sounds like it is coming from the top od the engine under the valve covers or somewhere near this location.
Where does the sound come from? Engine compartment? Front or back or maybe under the car, like the muffler/exhaust system.
The sound is coming from the area where the valve covers and fuel injectors are located. After the car is turned off the sound of roller bearings is heard for about two seconds. It can’t be heard from the drivers compartment, but if the hood is raised the noise is audible. It does not make any grinding noises only like something continues to roll on bearings. I have verified that the drive belt is stopped when this happens, so that leads me to believe that the sound is not any of the items that the belt operates.
The noise might be coming from a loose sparkplug tube that runs from the top of the valve cover down to the cylinder head. These are sealed to the valve cover and the head with a silicone sealant. If the seal has failed, these tubes can spin as the engine is running. As a matter of fact, whenever the valve cover is removed, the manufacturer recommends that the old tubes be discarded and new tubes be installed and sealed with the silicone sealant.
I have coil modules on top of the valve covers for each cylinder. Are the tubes that you mentioned underneath the coils? I will be removing them tomorrow and replacing the plugs , so I will have a closer look.