Weird sound coming from speakers after plugging in factory stereo

[ajmadic]

Hey guys, so I just purchased a used 2012 GMC 1500 from the dealership and was told by my buddy that works there he was going to have a new stereo ordered (since the one I have in my truck now supposedly doesn't work) but it was on back order at the moment. Being the impatient idiot that I am, I decided to pull my dash apart and check the wiring of my current unit. The unit was not plugged in, so I decided to plug in the first 2 left plugs (if you're staring at the front of the radio) then once I plugged in the 3rd, a horrible sound was coming from my speakers. I unplugged it immediately and the sound went away. Decided to unplug everything, then plug in the 2 right plugs then plugged in the 3rd one and same sound. I unplugged 1 of the plugs to make the sound go away, hopped on my phone to check the youtubes then I started to smell something burning. I grabbed the stereo (which was hot to touch) and unplugged everything then decided to put everything back together the way it was before I fu** anything up.

 

The previous owner had an aftermarket stereo system in the truck. Do you think the sound could be from the wiring being funky? Or from the actual stereo being fubar? I want a touch screen dash but didn't want to purchase it if the wiring was not done right.