Why is there a censoring sound in episode 6? In 11:25 of episode 6, there is a bleep sound, but I don't know why is it being censored. Jibril and Steph are surprised by it, so would it be a dirty joke or something else?
The Japanese text there is ま★こ ma*ko, which (to someone who knows Japanese) is obviously a censored form of まんこ manko, which does refer to the female genitalia, as Sukeibe points out. 

The key insight here is that manko is in fact vulgar slang for the female genitalia, which is why you will see it censored. The translation "nether regions" fails to capture this vulgarity, I suppose because it's constrained by the rules of word chain (can you think of a vulgar term for the female genitalia that begins with "n" and ends with "s"? I can't...). If a technical/medical term for the female genitalia were used instead (e.g. 女性器 joseiki lit. "female sex organ"), it would probably not have been censored.