My mouse is being stupid

Hey,
i have a issue with my MacbookPro i just have one since 1 week
and now i have a problem.
When i scroll with the middle button on my mouse my sound is changing but now i cant find it where i can turn it off. its really annoying me cause now i cant scroll down with the mouse on a website.

Does someone knows what to do with this ?

Thanks,

What mouse is it?

If it is a Logitech mouse, you can configure the scroll wheel in the Logitech Control Center (you can get there through System Preferences). Once open, click your mouse > Configure... > Buttons > Wheel and change the "assigned action". My guess is that it's set to "sound control" which will allow you to change the volume using the scroll wheel. Change it to "vertical scroll" to allow you to scroll up and down.