AW4 knocking, any ideas?

So I bought a 98 4x4 last night from a buddy, the trans went out about a month ago, he bought another aw4 and installed it him self. Trans is good, came out of a running driving jeep. I thought it was the bottom end of the motor knocking but it's actually the transmission making a knocking noise. It's only at idle, and comes and goes.

With that said, he ripped one of the lines off while wheeling so at this very moment theres no fluid in the trans, it will not pull at all. I have new lines to install.

Any idea what this knocking is that I'm hearing? Any idea if it's only because there's no atf in the trans? Sounds like it's coming from around the bell housing area. Just trying to figure out if this noise it due to no fluid or if the trans was installed wrong somehow. Thanks for the help!

Running an AW4 with no fluid will quickly destroy it, so do not do it.

Fix the line and fill her up . Wow. Check flexplate bolts i bet they are loose or maybe its cracked . My aw4 wont even move if its 2 qts low. You are telling us you lost all 8-12 qts that are in there?

The line was broken, we were able to rig it enough with a piece of vacuum hose to get it back to the trailer. It was leaking atf like crazy. Once home we pulled the lines and drained more out of it. I believe it to still be ok. It's just weird that it's knocking like that sitting in park.

Knocking coming from the bell housing is most likely a broken or loose flex plate

Flex plate bolts that aren't properly torqued will cause a knock. I had to re-torque a couple of mine after I replaced my tranny a while back.