Your truck might be haunted. Set up a video camera to observe overnight. Put some Laffy Taffy on the dash, they love that shit. You might lure them out of the vents to get some. But not the banana kind, those suck.
If it's ghosts, you'll probably need to call an exorcist. If you want to try DIY, then you'll want to have a seance and ask the ghosts what unfinished business they have on earth that's preventing them from moving on to the afterlife. But if the fix involves nudity and chocolate pudding, don't believe them. They're just putting you on.