i don't think its your rockers or lifters, i think you've got a bad bearing. If you arn't too mechanically inclined i don't recommend you investigating under the oil pan without someone who is. Just removing the oil pan isn't going to show you too much, the caps need to be removed, and if its not the caps, its your main bearings and that means you have to pull the whole crank. If that's the case a rebuilt might be in your future.
