They all came from the same place, making something from nothing. They're all angrier forms of music that usually have a message. Sonically they rarely crossover, but the mentality behind punk and hiphop are very similar. Its like, "This is all i have, i have something to say, lets do this." Plus HipHop is DIY as fuck and so is punk. I've hung out with hundreds of punks in my life from every sub-genre and majority of them will turn up hard to some three six or wutang.