What's scary is you don't know if there's a problem. The first time I started hearing ringing I called maintenance to tell them that my heating system was making noise. He came over to check and said he heard nothing. I thought he was crazy and then I asked several people in the building if they heard it. They looked at me like I was crazy and then when I went out I thought my neighborhood was going to explode. Then I looked it up on the computer and found out what it was. At night it's the worst.