I keep hearing this different sound in the middle of the night. It is so high pitched that, at first, I wasn’t sure I was absolutely hearing it, then but it is particularly there. It sounds love a absolutely high pitched whistle. I usually have the TV or my songs on when I am lake house during the afternoon. I believe that explains why I only hear the sound at night when I am trying to fall asleepâ€¦ Occasionally, it even wakes myself and others up when I am already asleep, then at first, I thought it was my refrigerator making the noise. However, after a bit, I realized that it is my air conditioner. I only hear the whistling sound when the compressor is on. I went outside but I can’t hear the sound when I get up close to the air conditioner compressor. I guess that the sound of the fans drowns it out or something; Maybe it can only be heard through the HVAC duct. I don’t know. I just worry that if I call for some Heating, Ventilation & A/C service, the serviceman won’t even be able to hear the sound at all. After all, my husbandy can’t hear it, he says that the whistling sound is all in my head but I guess it is there. I don’t want to waste currency having an Heating, Ventilation & A/C serviceman come out only to tell myself and others that my Heating, Ventilation & A/C system is good as well as he doesn’t hear any different noises; What if the sound absolutely is all in my head? Or, maybe I just received super human hearing somehow. Maybe this sound is normal for the air conditioner as well as I just couldn’t hear it before.