There is something fishy going on.
→  낌새가 이상한걸!

[예문]
A:Hey look, can you see the guy in the dark over there?
   저쪽 어두컴컴한 곳에 있는 녀석들 보여?

B:Yes,they are exchanging something secretly.
   응,뭔가를 비밀스럽게 교환하는데.

A:There is something fishy going on. huh?
   낌새가 이상한걸.