Some iPhone 6S users find problem with their phone audio. They reported that their phone audio is often distorted and the volume levels are gone wrong or error. Sometimes the turned up volume levels make a ringtones played through the wrong speakers and resulted as distorted ringtones sound.
On the other occasion, when the volume level setting is low, some sounds are ring louder that it could be. This problem is quite irritating because it will disturb the phone usage especially when the users have to customize it anytime they need to keep their phone in silent or in outdoor mode all the time they need to.
If this happen to your device, you can try to fix it by choosing one of these several potential solutions or try all of them until your problem resolved.
You can try to change your music setting by taping Settings, then tap Music, and choose EQ. Please change the settings available there, or just simply turn it off then see whether your problem could be resolved by this action.
Other option is by ensuring the cause of your phone audio problem, and if it just happen to the sound of specific app notification, the problem could be caused by that app is not fully updated. For the example, if you have distorted sound on the Skype app, it may be resolved after you update it completely.
Other potential solution to overcome this problem is by using the factory reset option in your phone. You can try to use factory reset option at your iPhone 6S but do not restore the back up because it is possible that your problem is caused by restoring old data in your phone. Please manually copy and move the content after you reset it.
Those are some potential solutions that you can choose to overcome your iPhone 6S problem. If those steps are still not working, please contact Apple, retailer or other place that can give any help to your speakers fault or audio distortion if it caused by the hardware problem.