When I was relaxing with my family and watching some TV, I decided it was a little hot in the house. So I got my phone and adjusted the temperature control settings via the smart thermostat. It was nice when the A/C came flowing from the HVAC vents, but I thought I heard an unusual noise. I asked my wife if she heard something strange, but she said she didn’t hear anything. So I just thought nothing of it, but then it seemed like the noise was becoming louder. I asked again if anybody heard anything strange, but everybody said they heard nothing. I thought maybe there was an issue with the cooling system, so I went to check the HVAC unit. It didn’t seem like there was anything wrong, but I did hear some kind of high pitch noise that seemed to be coming from outside. I went out there and it was the A/C condenser unit that was making this noise. I actually remembered cleaning out the A/C condenser in the spring, so it wasn’t blocked up or anything. I was trying to think about what the issue could be and if I should call up the HVAC company. Then I remembered something that was important. I realized that I forgot to change the air filter for the HVAC unit! So I turned off the HVAC system and changed the air filter. The old air filter was entirely filthy and blocked up really bad. I realized that was probably making the A/C system struggle quite a bit. When I turned the A/C system back on, there was no more noise coming from the A/C condenser unit!