[He was actually trying to be quiet, so there's not much noise until Rean knocks. Then there's a startled noise, strangled into an undignified squeak, and a splash as he jumps a little.]

Are you kidding me?!

[His voice is high and tight with surprise and fluster. Why does Rean have to be like this? Who just interrupts a guy's personal time to ask embarrassing questions?!]