I actually just discovered that as well -- it is when using the headphone plug. I also found out that it is due to European law:
"Under the new rules, higher exposure levels are permitted, but the user must willingly select them after being presented with a warning of the risks and ways to avoid them. How the warnings are provided would be up to the manufacturer and how it displays on the device's screen. Under the old rules, only a warning in the instruction manual was required.
EU standards are not mandatory, however it 'de facto' becomes the industry norm," the European commission said. "Products meeting those standards are presumed safe -– otherwise manufacturers have to go through costly independent testing for products. The new safety standards will apply only to future products."
It happens on my Blackberry Q10 also, everytime I open the Music App it warns me about high volume.
The other day I got a warning saying I have been listening to high volume for too long and it lowered the volume and then blocked me from increasing it. I couldn't even over-ride it!!!
fking politicians