Get a fridge with the highest efficiency rating that you can get, if you can afford it. As sound is simply wasted energy. A more efficient fridge will produce less sound. I have an "A" rating efficient fridge and is almost silent.
I haven't bought a fridge in a while, but I know fans (like built-in exhaust fans) have a sone rating, which is a measure of how loud they are. Maybe a PFer will know if fridges have these ratings, too?
Another place to look is a magazine like Consumer Reports. They would mention if an appliance makes an unusual amount of noise.
Also, user ratings are another source of information, albeit completely unregulated.