Samsaung Galaxy s5 volume increase after text message?

[AC Question]

When I listen to my music on my S5, through the speaker or bluetooth, the volume usually at first sounds somewhat low. After I get a text message with my phones volume turned on, the volume increases substantially. If I don't get a text, even with my volume all the way up it seems low until I get that text message because of the sound it plays which increases the volume right after for some reason. Does anyone know why this is??