SDL Mixer : volume changes - how do they work?


I have made a game, whereby the music plays in the background and some sound effects play when the mouse hovers over certain sprites. I noticed some change in sound volumes during this and I have some queries :

  1. Does the sound effect volume (Mix_Chunk) decrease automatically when the music (Mix_Music) plays?
  2. When the music is off, why does the sound effect (Mix_Chunk) automatically increase in volume everytime I hover over a sprite? The more I move over sprites, the more the sound effect plays (as it should) and the louder the effect gets each time. Is this supposed to happen?

Any help guys?

Many thanks!