I just bought an 00 Cherokee Sport 4.0 Auto 135,000mi. Yesterday it started a slight knock from the rear of the engine. With a stethoscope i can hear it most at the exhaust manifold from the #6 cyl. What could cause this?

 

Connecting rod, stuck/collapased lifter, bent valve, bad injector, exhaust leak, mis-aligned muffler bearings..........

 

Any of those. Or worse case, broken piston skirt. Muffler bearings ha ha!! Go to Youtube and search Jeep engine noises. They make all kinds! Good luck. Hope it's nothing too bad.

 

Oh, and welcome to the forum. XJs are wonderful! But like everything else sometimes ya gotta wrench on 'em. Good thing is there are plenty of knowledgeble people on here who have probably dealt with what you are going thru. So welcome to CF!