Dual alternator setup?

[Waterloo]

Yep, batteries and the alternator... How about your cable and grounds from the battery box? I had to replace all of mine a few years ago on my 08. I had cable with, in one case, nearly a foot of copper exposed to the elements at the starter, there was no jacket on it! The truck came from the factory like this! I reinstalled over 100 feet of power and ground cabling. That cured many issues I was having with the truck. May want to inspect those cables.

My stereo system, that I grounded to the sleeper cab with one of those fancy JL Audio ground lugs, you can use a stainless nut and bolt to do the same. I installed that ground behind the driver seat in the closet cabinet, right where the cab makes that turn to go into the driver compartment. I also ran a 2/0 AWG cable in at the same location to power the amps from the battery box. I have a group 31 dual deep cycle battery in there too hooked to a 500 amp battery isolator, it is tripped with the ignition.

I attempted to ground in other locations in the cab and sleeper and was getting noise or no ground.

What I did to eliminate noise, was to install Blue Sea fuse panels in the cab and sleeper. They are fed power with an 8 gauge cable. I used these and wired directly to the batteries. https://amzn.to/2C6yOwo
I turn everything on/off with these remotes. https://amzn.to/2NUdnkR
No noise...

And I am upgrading my alternator too, I just picked up a Delco 40si 300 amp unit, will hopefully install today along with new 1/0 cable. I'm leaving the original factory cable in place and running a second line directly to the battery box.

I don't really have any issues with the old alternator 165 amp unit, other than it is to small for the draw I have on the electrical system. This is something I have been wanting to do for some time, and with all new fresh batteries in the truck, I figured now is the time.