Does your truck have a CD/DVD player? I have a non-ram vehicle where the CD player/DVD will run for a bit (sometimes) after the vehicle is shut off. Faint high-pitched sound. Once ya open the door, it cuts the power and stops. But the CD player in my Ram doesn't do this ..that I've *noticed*.
Also, I heard a guy one time say ..the fin on top of the ram roof is a microwave communication device which sends a geo-loaction tag to aliens
in another galaxy. Which is why they built the James Webb Space Telescope. People with especially acute hearing (and certain animals) may be able to pick up on the high-pitched transmissions, but most can't. I should probably go on FB to confirm this stuff before letting the secret out.
Other than that, I'm out of ideas.