To dream of overhearing something represents feelings about becoming aware of what someone else really thinks.
To dream of overhearing something negative or that makes you feel jealous may reflect feelings about realizing the bitter truth. Feelings about realizing you have been deceived. Feeling that you have made a mistake trusting someone. Uncomfortable or painful signs of the truth being revealed.
Example: A young woman dreamed of overhearing her boyfriend say “we’re just friends.” In waking life her boyfriend had just broken up with her.