In this video, I go through 3 methods of making your hub sound louder and also how to make it quieter. You can use all three of these methods to make your hub extra loud. Remember that any hub modifications have the possibility of damaging your hub so only do this if you are sure you want to! This only works for SEALED hubs. Unsealed WON'T work because you can't remove the driver.
Personally, I like my hub a bit louder so people can hear where I'm coming from. e.g. When I ride to spots/skateparks people know I'm coming so they move out of the way for me. This works at skateparks as well, other riders can hear you coming so they don't snake you.