Bob the Interdimensional Trucker: Ghost in the Sky (Unabridged‪)‬

In Ghost in the Sky, the first installment in the Bob the Interdimensional Trucker series, Sam Gage has picked up an enigmatic motorist whose mere presence, it seems, is making Gage hear the sound of a small propeller-driven passenger airplane...or maybe even a crop duster. But whatever is really making the sound, which his rider can't hear, is not only keeping pace with Gage's truck at an impossibly slow speed for airplane flight - it's also invisible. 

Gage drops off his stranded motorist and the sound leaves with him - but now the second senior driver for Roads Unlimited is obsessed with the experience, and when he happens to run into the guy again he ends up trailing his former passenger down a rabbit hole filled with intrigue, deception and murder. And that rabbit hole might just kill Gage if he's not at the very top of his "dealing with weirdness" game.