Do you mean a constant high-pitch ringing in your ears? For example, when you’re lying in your bed in the evening and it’s quiet in the room? If so, this is just blood circulation. Your hearing became more sensitive, so now you hear it. It was always there, you just didn’t hear it before. It’s normal. It’s not limited to awakened people, some people hear this ringing, too. Everyone can hear it occasionally at times when the environment is just super-super quiet. You just hear it more often now, it’s not a big deal. I am hearing it now as I’m typing it to you. You get used to it.

If you’re hearing something else, it’s probably just your imagination.