A wagering game system and its operations are described herein. In embodiments, the operations can include determining an occurrence of an application event for an application that runs in association with a wagering game machine. The operations can further include accessing a custom sound source that includes customized sounds presentable separately from a soundtrack for the application, during a wagering game session on the wagering game machine. The operations can further include determining a custom sound, from the custom sound source, that relates to the application event and determining custom-sound presentation instructions associated with the custom sound. The operations can further include presenting the custom sound on sound production devices associated with the wagering game machine during the application event according to the custom-sound presentation instructions.