My air vents in my dining room have been recently making a squeaking sound when the heating and air conditioning plan turns on, then it has been driving me up a wall to be honest! I absolutely could not figure out where it was all coming from! Every time the heating and air conditioning plan would turn on, the air vents went squeak! At first I was thinking there may be a mouse in there or something like that, however but, I just had my heating and air conditioning air ducts checked as well as cleaned. I get my HVAC duct cleaned out every 3 months, and that 3 month time stage had just happened. I absolutely did not think 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, however 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, and 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 plan was trying to blow out a half closed air vent. This was making the noise! I was so glad I figured it out and fixed the problem. I was pretty close to calling a certified heating and air conditioning specialist to come have a look. I am so cheerful I did not do that!