knocking in engine after it warms up

Have 95 grand Cherokee 5.2 v8 that burns a little oil, but runs good. But when it warms up it starts to rattle, or knock during acceleration and only during rev up periods. idles quite. while it is cold it will not make a sound until it warms up. Timing chain issue or main bearings???? weird that it doesn't do it all the time. I can rev up while cold and no noises even while reving up. It is not the lifters...sounds come from front deep knocking while reving, let off it's quite. hate replacing things just find out it wasn't the problem....any ideas would be helpful. thank :crying: