Is loving to hear friends breathing normal?

Lately, two of my closest friends kept asking me to breath into the microphone (we live far away from each other, therefore we can't visit us very often and have to talk via teamspeak). They told me it's enjoyable and relaxing. After I sent them an audio video of people breathing on youtube, they told me that both of them don't want to hear anybody, but only me.

It also seems like they think it's funny not telling me why it's so great in their opinion.

Can someone explain me the reason for it being enjoyable?

(By the way, I don't think that they're actually using it as masturbation footage and they're not my boyfriends.)