So my friends 99 has been sitting for several weeks but has been driven intermittently for several years with no issues. Bangs the back wheels on first selection from park to drive. Fluid level good. once in drive it operates normal until you put it back in P and then bangs again into D. I forgot to ask if you go from N back into D if it does it. The engine is at normal revs for idle. Any fuses to check...Ive had 25 years of jeep experience but never once had any tranny issues. No check engine lights, if that monitors the tranny?

 

The first thing I would suggest is to put it in neutral and check the amount of back and forth rotation in the driveline without rotating the wheels. If it is a lot, that is the source of the noise. Common in well worn differentials

 

Thanks, will check that just in case in a few days when all this rain stops...She drove it around for a while today and now she says everything is working like it used to

 

Probably needs a trans drain and fill with the correct fluid.