have a false or hollow ring;
strike a false note. Seem wrong or deceitful, as in Her denial rings false—I'm sure she was there when it happened, or His good wishes always seem to have a hollow ring, or Carol's congratulatory phone call really struck a false note.
Ring false and the antonym,
ring true, which means “seem genuine,” allude to the old practice of judging a coin genuine or fake by the sound it gives out when tapped. This practice became obsolete when coins ceased to be made of precious metals, but by then the idioms were being used to refer to other matters.