2000 Jeep Laredo Noise in engine

This is a common problem with the 4.0 engines. After 100,000 or so. They are known for minor piston slap and carbon build up. Go to your local Chrystler/Jeep dealer in the parts section and buy a can of MOPAR combustion cleaner, this is one of the most effective carbon cleaners around. It costs around $7.00 a can and read and follow the directions, if this does not fix the problem, your heads may need rebuilt. Just to let you know, the 4.0 engine will run thousands of miles with this minor knock in the engine (assuming this is what you are talking about). If you are hearing a knock in the engine that gets noticeably louder as you rev. The engine up, then it could be a rod knock and the engine may need a rebuild. BUT if it is the noise where you hear a knocking noise but does not get louder as you step on the gas, this is not a rod. I had a Jeep make a knocking noise and it kept good oil pressure and after cleaning the combustion chamber, it was still there.I drove it like that for another 150,000 miles. Hope this helps