It turns out I wasn’t linking the lib files correctly. I was missing the linker flags in my Xcode configuration.
Add “-lfmodL_$PLATFORM_NAME” and “-lfmodstudioL_$PLATFORM_NAME” to “Other Linker Flags” (in the “Linker” section)
It was weird because things appeared to be working fine even though I apparently wasn’t even linking the FMOD libs.
The post from markmarijnissen at http://52.88.2.202/questions/question/forum-39077 helped a lot on how to correctly set up FMOD in an Xcode project.