Double check your oil pressure. Do you change the oil and filter regularly?You can use a long shank screwdriver or maybe a long lug-wrench, place the the tip where you think the noise is coming from. Be careful, don't get anything caught in belts--pulleys--fan, you --your cloths--the tool. The other end of the tool you place on that bone backside of ear, helps to magnify the sound. Your close to the problem where-ever it sounds the loudest. Try it on your valve covers and oil pan.