Thats super cool, some of the issues you may need to address before this becomes too cool.
1. Prevent people from advertising, ok this can be a revenue model also :P
2. Allow me to shout to places other than where I live, like suppose i am visiting a new place. It will be cool to shoutt at the new place before I reach. Though this is not necessary, just a thought.
3. Some kind of block list where I can block certain noisy neighbors whose shouts I dont like.
4. Someone shouting for needing security or SOS, can be highlighted, people around should receive these help requests on priority basis. Can help prevent robbery, protect women from potential harrassments.
Overall this can bring communities together, glue them. Wish you luck with the startup.