Whining noise, code P1870

I bought my this vehicle listed above about two months ago for $500.00, now I know that there are problems to be expected because it did sit for a few years before I purchased it. I have a whining noise underneath my hood it sounds like power steering but not exactly. I know it’s not the power steering because I turn the wheel back-and-forth and there’s no up n down power steering whining noises, I checked for leaks and the power steering fluid is full and clean.
The noise is constant. Could this be my air-conditioning unit because I filled it up at the beginning of the summer and it still does not blow out cold air.
I just replace the idler pulley because it was warn out thinking that that could be the problem but the noise is still there and getting louder.
The vehicle runs amazing other than that noise, I was also wondering if it could be the drive box because I’ve had to replace some parts on the front end as it was wearing out the insides of my tires. The noise seems to be coming from some sort of component and not from the tires or anything to do with the steering, it sounds like it’s on top of the motor.
I am replacing the shift solenoid for one and two on Saturday because it shifts hard From first to second gear after the truck is warmed up when it’s cold it doesn’t do it. The code came up P1870, Could this have something to do with it?
Possibly torque converter or transmission pump?