Back of phone vibrating when sound plays

[felix400]

I just bought a brand new Samsung s5 mini and have noticed that the back of the phone vibrates whenever there is sound playing, as if the back cover is loose or something (I checked and double checked though). So it's not a vibration setting, it's the phone vibrating from the speaker, I think. It happens if I play music, or an app has music in it, or I'm watching a video, etc.

Just wondering if this is normal or if this shouldn't be happening.

 

[sydneycooper1979]

Hello! Do you have the volume turned all the way up?