I am "feeling" a new vibration. I first noticed it while driving, but it is definitely noticeable when I put my hand on the valve cover with the motor running. It is sort of a low frequency, (not audible and not quite a knock), very subtle vibration at this point. It seems to me that there are three possibilities: external on the front end, (water pump or fan/pully?), external on the rear, (clutch or flywheel), or internal, (rod bearing?)
Any hints on trying to narrow this down?
