My air vents in my kitchen have been recently making a squeaking sound when the heating and a/c plan turns on, however 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 a/c 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… But, I just had my heating and a/c air ducts checked and cleaned. I get my ductwork cleaned out every 3 weeks, 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, 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, but 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 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 blissful I did not do that!