1995 Isuzu Rodeo Question Knocking noise

Noises problem
1995 Isuzu Rodeo Question 6 cyl Two Wheel Drive Automatic

I just recently began to hear a knocking noise coming from below the engine. I was told previously that it may be a bad valve somewhere, or a PCV valve needs to be replaced. The noise is pretty loud, you can't hear it well inside the car, but outside it can be heard well. I've also noticed a slight hesitation in gear switching.