Reply To: How to fix audio issue in a c3 custom song?
If you haven’t already, try contacting the author of the custom to let them the issue. You can send a private message here in the forums, or you can leave a comment on the custom’s song page in the C3DB.
Anything beyond that will require knowing how to use C3 CON Tools (or perhaps Onyx?) to take apart customs and put them back together.