Noisy Tow Vehicle

[Baldicon]

I have a 2017 Ford F350 diesel dually with the factory puck system. Bought it to travel, but have less than 20k miles. It has developed a very loud squeak, which is getting worse. And, it only makes the noise when I have the 5th wheel trailer (Montana 3121RL) connected. When unloaded it does not make a peep. I have a B&W companion hitch with a Trailair pin box. I lubricated the hitch and pin box and torqued all bolts, and adjusted the hitch locking cams. My son-in-law rode in the bed of the truck around the campground to see if it was the hitch or pin box, and he said neither made any noise and the sounds were definitely coming from under the truck. While he was in the bed of the truck, I crawled underneath with my phone on video, and he rocked the truck from side-to-side and it sounded like an old rusty box spring being used for adult purposes. It’s embarrassing to drive through the campground. So, I called the local dealer to schedule an appointment to get it looked at, and the scheduler asked if it made the noise with out the trailer and I told him no. His reply was that he didn’t see how they could diagnose the problem. I told him I would bring the trailer down there or they could put 3500 lbs in the back of the truck. I will do anything they ask to help get this fixed. He said he would get the service manager to call me, but he hasn’t yet. Any thoughts on what it could be? I can’t tell if it is suspension related or possibly something in the puck hitch system. But either way, it is totally unacceptable for this new of a truck to sound like a 30-year-old garbage truck. Any help or advice as to how get it resolved will be greatly appreciated. I have a feeling that I will have a battle getting them to fix it.