訳わけがある

expression, godan verb (-ru, irregular)

have a reason; have an excuse

Used when there is a specific reason or justification for something, often implying that the reason is not obvious or needs to be explained.

• 彼かれが遅ち刻こくしたのには、何なにか訳わけがあるに違ちがいない。

  There must be some reason why he was late.

• そんなことを言いうからには、訳わけがあるんだろう。

  Since you say that, you must have a reason.