Clairaudience

Clairaudience is the psychic ability to hear what people outside natural hearing range are saying inside one’s mind. This is merely an aspect of another psychic ability such as Empathy or Sensing rather than a seperate power.

Empathy
"I can't. The pain. The noise."

- Prue to Father Thomas.

The power of Empathy enables the user to feel/channel other people emotions. However, some users can hear what people outside natural hearing range are saying.This is a by-product of channeling their heightened emotions.

Mortals not destined to have the power of Empathy will fight against the emotions and the voices they're hearing. However, this will slowly drive them insane, and will ultimately kill them unless the power is withdrawn. However, with guidance from a true Empath a Mortal can learn to control the power, turning it on and off at will.

During Prue Halliwell’s brief time as an Empath, she was able to hear the arguments people were having all over the city. This was due to Prue’s Empathy picking up on the intense emotions behind the angry words people were shouting at each other.

While Mortals can learn to embrace the emotions and the voices connected to them, demons will not be able to. The crushing weight of human emotions and the voices connected to them will drive a demon insane, but not kill them. Vinceres is a prime example of this, he was driven insane but was able to fight the effects to stay alive.

Sensing
A unique aspect of sensing used to hear what people outside natural hearing range are saying inside one’s mind, while sensing their locations.

Only Whitelighters and Cupids posses it, their sensing power enables them to hear the "call" of their charges whenever they are in need, allowing them to go to them when they need them most. They can put charges on mute when they wanted to, just like Chris did when he heard Phoebe calling for him.

In "Siren Song", Piper is given Leo’s powers, including the power to sense his charges. Using this ability, Piper could hear Phoebe calling out to her for help. It is most likely this is the aspect of a Whitelighter's sensing ability that allows charges to communicate simply by calling their name.

Note

 * This power is not to be confused with Telepathy (the power to hear someone's thoughts) or Super Hearing.