Where is the quietest seat on an airplane? Ahead of the engines, you will find the quietest seats. Upper deck (on Boeing 747 or A380 aircraft) over lower is recommended for minimizing noise levels. However, mostly the noise will be determined by how many babies, rowdy passengers and how close you are to the bathroom. Baby cots are usually placed on bulk-heads at the front of the economy section so avoid this if the noise will bother you.
The best bet for minimizing noise levels is to use earplugs and/or headphones. You can wear the headphones while you sleep tuned to music channel that suits you best. Also consider investing in noise reduction headphones. Click here to learn more about noise cancelling headphones.