Odd ? My 96 explorer makes knocking sound while in drive when I accurate it goes away, and the explorer shifts and runs perfect .

Can you tell where it is coming from, engine, tranny suspension etc,?

Sounds like its coming from the bottom between the engine and tranny.

Possibly check flywheel. Also look for loose brackets and braces that sort of thing...

Which brackets and braces

Does it only do it while driving and never while in park?

Does it a little in park but mostly in drive

Searching for noise without a stethoscope is tricky. But it can be done by use of a dowl rod, placed close to your ear. The louder the noise it gets, the closer you are to the scorch of the noise. If you have to put it in gear, best to have a friend to apply brake, or block wheels, apply emergency brake. Then you will know the area.

Could be any one of them you'll have to get under it and start feeling and looking around.

Is the sound rythmic with the speed of the engine? When in park, if you increase the rpm's slightly, does it increase also? Check all the mounts for the engine and tranny. Sounds like something is loose and when the engine speed increases the torque of the engine may take up the slack of the worn or loose mount.

torque converter coming apart internally,