You may have HDR+ enabled which means the camera takes multple pictures and thgen processes, so taking many shots quickly in row won’t work as you discovered.
The sound is a different issue, I’ll look for a link but you can check for ‘audio clipping’ etc. It seems a lot of sounds are ‘too’ loud and audio is clipped etc.
You may also like to try Open Camera for the sound. It has a lower volume and doesn’t clip.