Need advice on engine making a new sound.

[Magdump]

I have a 97 Jeep XJ. I replaced engine about 1500 miles ago with a remanufactured engine. It has been the quietest 4.0L I've ever heard. It didn't have a click rattle or knock since it was installed. Recently when the engine was at idle with 55 lbs of oil pressure you can hear a deap bottom end knock like a rod. It has never been hot and I only run Lucas high zinc 10w30 oil and Wix filters. I've changed it 3 times in the 1500 miles. I'm not confident with all the cheap Chinese parts out there. I've seen so many cams and lifters eating themselves alive. So far I hadn't seen any metallic specs in the oil. Im going to start unplugging injectors one by one to see If it changes anything. Has anyone had this problem? Do some 4.0Ls just make bottom end noises?