Hi,
if you want to stay at the airport itself, I would recommend the Yotel. This is under the South Terminal. it is small, but very clean and comfortable, and not expensive (think I paid around £55 for the night). The only noise is from doors closing, which you can get in a hotel too. google "Yotel" and have a look. The hotels linked directly to the airport are very expensive. other hotels you would have to pay for a taxi or shuttle bus, so doesn't always work out cheaper.
Hope this helps