If they are bad, it could cause enough slop that the piston slaps the valves. You did say this: The rattling is semi quiet at idle but gets louder and consistent when it gets hot. The rattling sounds like its coming from the right side of the motor, near the bottom. If you are hearing noise in the bottom end and it has been run hard on low oil, I'm guessing rod bearings. Disclaimer: I am not a doctor, lawyer, cop or mechanic.