engine noise was number eight bearing failure

most likely due to some junk in the oil, but no idea where it could have come from. The engine looked like a decent, clean rebuild, but only got about 12K miles. Only symptom was a weird rattle that only occurred under some load conditions or briefly when revving the engine while in park. grounding the number 8 spark plug wire made the noise go away, so we knew 8 was the one to look at.