HP Pavilion 15-p046na Audio :: Sound Level On Playback?

I've recently bought an HP Pavillion 15 laptop with AMD/Realtek HD audio hardware and Beats Audio. Windows 8.1operating system.  It's brand new out of the box with no updates made.
 
When I playback mp3 music via Windows Media Player, the volume is getting boosted during quiet parts.  This is especially noticeable on tracks which fade out, the sound level gets progressively higher as the song fades out, like it's trying to maintain a constant playback volume.  This creates a lot of background noise on music recorded from vinyl, for example.
 
I've checked it isn't the recording, by transferring the same mp3 file to another device and playing it there - the song plays back exactly as recorded, no problem.
 
I can't find any options in the audio devices (or beats audio) which might control this behaviour.  Is there an equaliser somewhere in the system?
 
p.s. it behaves the same even with Beats Audio disabled. p.p.s it behaves the same with internal speakers, headphones and external speakers.