Both are vastly different: 그런데: by the way 그러는데: according to [someone]; given to that 그런데 집에는 언제 갈 거야?: By the way, when are you going to go home? 엄마가 그러는데 오늘 저녁은 외식할 예정이래: According to mom, we are going to eat out this evening.