20 at idle doesn't sound bad. We always get a kick out of listening to a video of the noise('s).....I did it once with U-Tube, wasn't too hard.

Lifters on the 4.0 can make a pretty solid knock. Also if it's badly carboned up maybe just runner' a bit might clear it out some.

A rod will sound worse say, pullen a load up a hill, putten it to work.

 

Alright guys, I drove it around a bit, gave it seafoam, and have new results.
It's knocking still, its also running about 5-10psi for oil pressure....
It's got 1 quart too much oil in it.

Would the engine being overly full on oil cause it to foam the oil and let the pump lose its prime? Seafoam did nothing for her...
The knock is not there at idle, nor at 3,000 rpm, it dominates at 1,500-2,500.

I'm ready to drop the pan and prime the pump and lower the oil level if that's what it takes, just need some input... Very close to buying another xj and swapping parts