97 Jeep Grand Cherokee making knocking noise ideled and while accelerating....?

It sounds like the mechanics already have it figured out. Probably a rod knock. This might cause low oil pressure also. Your are already close to a quarter million miles, so figure out your next step. Either start saving money for an engine or a new vehicle. In the meantime you could get the oil changed to something heavier like 20w50, it will quiet the knocking some. I would not normally recommend that heavy of an oil, but it might buy you some time if your engine is going out. You still might get years of use if you take it easy and not abuse it.