There are a lot of examples where people are hearing voices. This is making me wonder if it is some sort of cultural reference to something in Poland, or if Polish people regularly hear voices
I think it must be the creators' sense of humour, although maybe I am not aware of something ;)
They're synonyms, but only "kiedy" can be used in questions. It is not limited to questions though.
Hmmm... I think that would be a bit of an overinterpretation. It would need "zawsze gdy" (always when).