I have a 390 with a recent rebuild - less than 500 miles. Immediately after first oil change it started making a ticking noise . Sounded like a bad exhaust lifter at #7 cylinder. Replaced both lifters for #7 but noise is still there. Loud at idle but gets more quiet as RPMs go up. When I pull the #7 plug wire when the engine is running the noise stops. I understand it might be a rod bearing but the noise is a metalic tick, not a lower end knock. Any idea's before I pull it apart?