There is no such thing as a quiet A/C as of yet, but there are quieter models and noisier models. If you look around, you can find the ratings for some. You have to include some of the keywords such as "quietest" "db" "noise", etc. I can look at my model when I get home, it was the compromise I came up with.
There's also lots of things you can do like: Putting an absorbing sound barrier directly betwen you and the unit (without blocking air flow and overall circulation, of course, so "line of sight" only). Putting a cushioning between the unit and the window frame all the way around to prevent sympathetic resonances, vibrations, and buzzes. Making sure it fits snugly. The fewer extraneous parts to fill out the window and add to potential things to loosen, the better.
That said, these things are pretty darn quiet, and make a small but tangible difference through the evaporation of water.