Kate would point out that she can hear them, but one, Phoebe's kissing her deep enough that talking's not an option (not that she objects or wants the option, since she's kissing back as deeply as she can while leaving her arms free for Aidan), two, Aidan undressing her's never not gonna be hot, and three, if one of them doesn't get her out of her clothes, she's gonna do it herself. So, it's all win and no lose and Kate goes really fucking willingly along for the ride.