noise

Hi,
In the last few days my 2014 cascadia developed a noise. It sounds like tires when you roll the window down but much louder. It starts at 55 mph and gets weaker faster i go. I can hear it more when with a trailer or under load. More likely coming from the back but not sure. When cruising and giving it more gas the noise gets louder. Moment i get my foot off the pedal it gets weaker. Under 55 i barely notice it. Truck has 400k miles on it and i am pulling tanker. Any ideas please. Thanks

 

Lets say i go 60 on flat. The moment i press gas and create more torque it gets louder. Its louder under torque

 

Yes, before this noise started i had vibrations once in a while and only with some tandem trailers and only between 34-50 mph! I thought this was the trailer problem. This noise that i hear is a humming noise. Low frequency hum

 

Engine fan starts and stops like it normally does

 

So i shut engine off while driving and noise is still there. But its so weak that i am not sure. There is tires hum and something else on the background.