Okay this has been driving my family buggy. When we first bought this house 5+ years ago I think it had a 3 ton unit for a 1,800 sqare foot house. At the time A/C was not that noisy. We knew we were having to do an addition to the house but in the intrum we had the A/C conk out on us about 2 years ago and we decided to go for a 5 ton unit that would be able to support the addition as well (which has not been done and probably is about 2 years off from architect to conception). Since this new unit the A/C has been LOUD. I am not taking mechanics or ratteling or anything it is just pure wind velocity noise. If I close the vents in any of the room the partial closing makes the vents whistle. On a few of the older vents they actually just can stay open or if I put it 1/2 way it just snaps shut (I assume to the force of the air as this will only happen when the air is running). Its great to have a cold house but how do you get it so you don't feel llike your in a wind tunnel every time the A/C turns on? I read somewhere to get bigger vents? but what size should I go to most of my vents are already 13x13 square and quite large.... ON a side note if it is purely the tonnage of the unit an the square footage it can handle can I assume since were adding 1/3 the square footage the noise level will also reduce about 1/3rd? I am so frustrated with this noisy house.