Quick test: get some electrical tape and put "tags" on the back stay every few inches, and at different angles (maybe every 60 degrees or so). This will break up the airflow over the backstay and should disrupt the tone produced. If it's not your back stay, then the tone will continue.
As to what you do if it is the backstay: perhaps add some cable shroud protectors to make the backstay cables bigger and thus disrupt the flow, or foam, or zip ties.
If I die, my biggest fear is that my wife sells all my toys for the price I told her I bought them for...