I did an oil change on my wifes car. I noticed a SLIGHT sound coming from the bottom of the engine. It sounds like a rod knock. Keep in mind it is very slight. Would this me normal or is the engine possibly on its way out. I noticed it while checking under the car for leaks after an oil change, I left the motor running. I normally shut it down when checking under the car, so I never noticed this before and it could have been there since new. Car has 72k on it purchased new. Oil changes every 3-4k. conventional oil. I have a Super Tech filter on it.