Got a knock, hoping for the best.

I picked up a 97 XJ 4.0 from a friend at work. It needs a leaking freeze plug on the back of the motor replaced. I changed the oil (10w-30) in it a couple days ago and have notice a knock coming from the bottom end every since. I put a piece of rubber hose on the pan to listen and it was the same as on the bell housing. I need to drop the trans to replace the freeze plug but do not want to mess with it if the main or rod bearings are going out. I pulled each plug wire off one at a time while running and the knock did not change. It does it hot, cold, nuetral, in gear, and increases with motor speed. I am hoping it is the flex plate but is there any way of being sure without dropping the trans? Thanks everyone for the wonderful site!

You can inspect the flexplate and check the tightness of the attaching bolts, which are known to come loose, without removing the trans.

x2 on checking the flex plate bolts. How loud is the knock? Theses engines can just be noisy. My 1995 ZJ 4.0L has had a knock for the past 100,000 miles.

Also, check the top end. Could be a valve train issue. Engine bays tend to send sound all over the place.