Foam/Spray Insulation

I live in a center unit townhome, which is about 8 years old. I am convinced there is little to no insulation in the walls between my neighbors' homes and mine. I can hear most conversations, children running and playing, and the dog barking at all times. I want to know if there is a way to spray some type of insulation in already constructed perimeter walls. If so, how is this done and what are the costs I can expect?

Any help would be appreciated to preserve my sanity. THANKS!!!