Hi there
After two days the message still didn't get any love. And all it took me to find out, was less than a minute of google search.
Google Search for:
Galaxy s4 sound warning when increasing volume
The very first post has an answer and successful fix, which I tasted, and can confirm, worked for me.
Quote:
" went into music settings and checkmarked the option to set all songs to the same volume. Now when I increase the volume, the warning message doesn't come up at all, and I can increase volume to the maximum if I want. Finally, I've been trying to fix this problem for ages, and I know others are experiencing this as well! Try this out and give me a shout if it works for you "
See, google is your friend
cheers