Engin knocking or valve tapping on 1999 Jeep Grand Cherokee

Engine has tapping noie. sounds like valve lifters

A tapping noise from the engine can be from any number of causes, ie: piston slap (excessive clearence between piston and cylinder wall), lifters, injectors, carbon buildup on piston tops etc. I suggest you take your vehicle to your local repair facility for inspection and diagnosis. here is a link to shops in your area: