The issue here is the impedance difference between your Lumia 525, and the headphones (MDR-AS200).
Lumia 525 jack: 8 Ω speculation, see comments
MDR-AS200: 16 Ω
Your issue is a typical situation where the device that transmit the audio signal over the jack has a lower impedance than the speaker.
This usually results in what you ...
If you can pause it, pause and cancel it.
Else go to Settings->System->Storage->Phone Storage->Apps. Uninstall Equalizer from there. Open store and check for updates.
Now restart the phone. After some time(for it took more than a day) reinstall the Equalizer app it will install without asking for hardware limitations. You can find the Equalizer app in My ...