In George R.R. Martin's A Song of Ice and Fire series, the author devotes a lot of time to fleshing out and differentiating between the various personalities of Daenerys' three dragons. HBO's Game of Thrones has done the same, albeit to a lesser extent, choosing instead to focus primarily on Drogon, the largest of the dragons.
In both the books and the television show, Drogon's depicted as the strongest and most aggressive of Daenerys' dragons - appropriate given his namesake and her suspicions that he's Balerion the Black Dread reincarnated. Though temperamental, Drogon is also the most closely connected with Daenerys, something that Game of Thrones sound designer Paula Fairfield wanted to incorporate into the noises he makes. In an interview with WNYC's Radiolab, Fairfield explained that because Daenerys sees Drogon as an extension of Khal Drogo, it made sense for the dragon to click and chirp at her in a way that was almost flirtatious:
"I have sounds I might choose simply by certain personality traits that I want to put forward. So in the case of Drogon - she named that dragon after Khal Drogo, her hot, late husband - and so Drogon is like her lover. He's whistling at her all the time, he's looking at her butt and going 'ooh, baby.'"
As Drogon's grown larger over the seasons, the sounds he makes and the way Daenerys interacts with him have changed drastically - something Fairfield carefully factored into her work. Though the dragon doesn't chirp much any more, Fairfield made a point of giving Drogon a distinct purr that would manifest during moments with Daenerys to indicate their closeness. And just what real-world noise is a dragon's purr based on? Tortoises having very loud tortoise sex:
"The groan of the male actually became - with some work and adjustments and stuff - the source for Drogon's purr with Daenerys. The funny thing about the purr with Drogon was watching people watching [the show] and giggling when they heard it, but not really knowing why. To me it's because it had that essence - that kind of sensual, sexual essence."
So hey, maybe you've caught yourself feeling some type of way while watching Drogon sweep through the air and breathe fiery death onto Daenerys' enemies. Maybe you thought you just had a thing for queens in fantastic coats. Maybe, though, just maybe? Maybe you're kinda into tortoises.