Is it a mitzvah to “guard” one’s hearing the way one is supposed to “guard” one’s tongue?
Regarding the specific prohibition of spreading slanderous speech, the prohibition applies equally to the speaker as well as the listener. This means that one is not allowed even to “just” listen to slander. When one hears such forbidden speech, defending the person being spoken of usually doesn’t help, and often it makes things worse since the speaker will only further justify his remarks. Rather, he should politely change the subject. If that doesn’t help, he should find a way to end the conversation or leave. If that’s not possible, he should make every effort not to hear the bad talk or at least not accept it.
This guarding of our hearing is part of a more general attempt to guard all of our senses from physically and spiritually harmful influences, with the idea of sanctifying ourselves with holiness and purity.
If the body is likened to the Temple, the head is like the holy menorah in the inner Sanctuary. Just as the menorah had six symmetrical branches from a central stem supporting a total of seven vessels, so too the eyes, ears and nostrils are symmetrically located around the mouth forming a total of seven apertures in the face. Accordingly, our intellect is the pure oil that flows into and illuminates these holy vessels. Just as the Temple in general, and the Sanctuary in particular, had to be guarded from impurity to maintain their sanctity, it is extremely important to keep our bodies, senses and minds free of impurities. Only then can the intellect burn brightly through our senses and illuminate goodness and purity into the world.
There are many examples of tzaddikim sanctifying and thereby sensitizing their senses, making them privy to normally extra-sensory information. Here’s one about hearing:
The great Rabbi Zusha of Anipoli initially wandered anonymously around Europe in a spiritually motivated, self-imposed exile. During one of his journeys, he was sitting in the shul of a small town when a woman emotionally burst in looking for her husband. She explained that he had suddenly left her without giving her a proper bill of divorce and that she was roaming the country in search of him. Rabbi Zusha calmed her down and told her that he was in the local inn of that very same small town. Everyone rushed to the inn, and sure enough, there she found her husband.
Years later, responding to those who marveled how the Rabbi, far from home, not knowing a soul in that small, remote town, knew to direct the forlorn woman to the inn, Rabbi Zusha explained: “All my life I guarded with great care to hear only good, spiritually beneficial things. G-d thereby protects me to hear only such things. That morning, I passed the inn and heard a man say he was so-and-so from such-and-such a town. As I was reflecting on how I wouldn’t hear such a trivial, mundane matter for nothing, the woman came into shul…”