@Saiangeli
They were pretty roundabout about it but they DID say that using metal ki is bad and will mess with your brain. He also just saw how crazy the other metal ki guy is, and even said to himself "ok this might have driven THAT guy crazy, but I'll be careful"
It's also not unreasonable that even just the little bit he's used it before meeting the old lady has already made him somewhat addicted/influenced by it.
Plus even on top of all that, Noh is a stubborn asshole and doesn't like to listen to anybody until getting beaten down at least a little, whether physically, verbally, or both. He doesn't know these people and has no reason to trust them, especially since he was brought there by an elder from a rival organization/clan/whatever the deal is with the people he was semi-captured by.
If anything I'm just glad that the huge slog with the metal ki god guy is finally over, that shit took forever. I'm hoping the plot picks up the damn pace a little.