There’s a decade-plus-old Cadillac CTS parked in an alley next to the studio. “I got it washed four days ago,” Mars says proudly. In a way, it’s become one of his closest musical confidants — he’s mixed every album he’s put out since 2010’s Doo-Wops & Hooligans by listening to it inside the Caddy, getting a sense for it in the sort of real-world scenario he deems optimal: A pimped-out American luxury sedan so old it has a CD player.