My 1994 Nissan hb 2.4l has a light and unsteady tapping knocking sound where transmission meets the engine. A metal rod or wooden rod picks up nothing as a stethascope. I can only hear it using my ear. I just hear smooth rolling sounds when listening with a rod against the entire engine and transmission unless placed against the stick shift while sitting in the cab. Its very faint unless underneath the transmission. Cannot be heard above idle. Revving the engine does not result in any knocking. Adding lucas oil stabilizer did not affect the sound at all. Used 1 quart, 10 w 40 casrtrol oil, 198,000 miles.