I recently got a new heating system plan and the brand new device started making a whistling sound. I thought that was how heating system devices operated until our brother complained about it. He told me that a heating plan making a noise meant something bad. Since the device was brand new, I was absolutely angry at the thought of it already being messed up. I looked online and found that a clogged heating system filter could be the reason for the whistle noise. The reason the sound happens is that the airflow is being stopped in the system. The air filter could be the cause because if it gets super caked on with dust, no air can get to the system. So the heating system has to find a way to move air in a unusual location and this causes a whistle. I evaluated the Heating as well as Air Conditioning filter and it looked fine. Even though it seemed clean, I did buy a whole new a single and that did not repair the issue. I then looked into other possible complications and a single was that there is a gap in the air duct. A small hole between the duct and the heating system blower will cause a loud sound. I looked all around in our heating system plan and even had our brother take a peak, the two of us could not find a gap. I finally called a Heating as well as Air Conditioning guy into the home to see if the two of us missed something. The guy instantly said the issue was that our ducts were absolutely too small for the heating system device. The heating system needs greater ducts for greater airflow. So that was an extravagant appointment.