That's the price we pay for services, they have to go somewhere! It's the same with power plants, water facilities and tips. I live right next to the airport and I don't have a problem with the noise, you get used to it and I don't even notice it now. I knew about the airport when I bought my house, as did people purchasing/renting properties in Stockport.
The difference here is, people living in Knutsford before the second runway was built may not have known about it, and may have chosen to live elsewhere if they had known. Any new residents moving in know what they're getting, and in my opinion, they should not be compensated.