What tests can I run at home before going to a repair shop?
Start with the Fix My Speaker eject tone to rule out moisture. Then play audio at different volume levels and note whether the distortion is consistent or varies. Test both the earpiece and the bottom speaker separately. Record a voice memo and play it back to isolate recording issues from playback issues. If all of those tests point to the same output problem and multiple drying sessions did not help, hardware fault is likely.