Photo credit: moneysaver67 from morguefile.com

1. Word got out about your neighbors loud parties
2. Word got out about how loud your neighbors are in their bedroom at night
3. You're close to an airport
4. Loud animals nearby
5. Commuter trains running nearby
6. Close to a highway
7. Neighbors that love to use their tools -- drills, chainsaws and sanders
8. Noisy motorcycles and car start-ups every morning.

Conclusion:  Sell your home when your neighbor is on vacation

Source