Hey there ByronBears,
Thanks for reaching out to the Apple Support Communities. To get started, are you only experiencing this issue when listening to music through the Pandora app, or have you noticed if other apps have experienced the same issue? Does the issue occur when not using an auxiliary cable, and just listening to music through the iPhone speakers?
If only having issues when using the Pandora app, give the steps listed in the following resource a try that can help with troubleshooting this issue: If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open - Apple Support
While we understand your not having issues with the app not opening or not responding unexpectedly, the steps above can help with troubleshooting other issues you may be experiencing with a third-party app as well.
Also, do you by chance have another auxiliary cable you can test the issue with? If so, give that a try as well as this can help with narrowing down the issue further.
Keep us updated on the results.
Take care!