My air vents in my dining room have been recently making a squeaking sound when the heating and A/C method turns on, but it has been driving me up a wall to be honest! I entirely could not figure out where it was all coming from, and every time the heating and A/C method would turn on, the air vents went squeak! At first I was thinking there may be a mouse in there or something adore that! But, I just had my heating and A/C HVAC ducts checked and cleaned. I get my HVAC duct cleaned out every 3 weeks, and that 3 month time period had just happened. I entirely did not suppose what was going on! I went and checked the air vents in some other rooms, and none of those were making that high pitched squeaking noise. The more I looked around, I finally figured it out! It happens to be that I had the air vent closed off! There was this little switch sort of thing! All I had to do was pull it, and the air vent would open and close! I stood up on a chair and pulled the switch. Then, there was no more squeaking! The air from from heating and cooling method was trying to blow out a half closed air vent. This was making the noise! I was so ecstatic I figured it out and fixed the problem. I was pretty close to calling a certified heating and A/C specialist to come have a look. I am so cheerful I did not do that!