Why are Air Conditioners so freaking loud?

Recently moved into a non-central-AC house and bought two brand new window unit air conditioners of different brands of average quality. Less than a couple months into use, it seems they got louder? How do people sleep at night with this vacuum-cleaner sounding thing? Haven't window units been around for decades? It's 2011 and they still sell the same old heavy noisy units except with a digital display and efficiency setting Why hasn't any of the manufacturers fixed the noise issues?What is in those machines that make this kind of noise?