I was towing 19000 lbs with a 2016 ram 3500. I got an intermittent service 4wd

What is your question?

The truck was making high frequency noise that changed frequency as the AISN transmission shifted. It doesn't Make the noise when it is not towing. To get the noise the load is heavy and changing road grades. Since it changes frequency as the transmission shifts I've ruled out the engine and turbo charger. Dealer has no idea. What about transfer case?

What makes this problem better or worse?

Towing and going up and down grades

How long has your 2016 Ram 3500 had this problem?

1800 miles