In Plasma 5: System Settings -> Audio -> Configure Volume Controls... -> uncheck Audio Volume under Show visual feedback for changes to:. I know it's not the o

In Plasma 5: System Settings -> Audio -> Configure Volume Controls... -> uncheck Audio Volume under Show visual feedback for changes to:. I know it's not the only issue you have, and not all of them will be solvable, but I found this solution quite quickly (though I did search for volume in the notifications settings first, which didn't show me anything). Also, if you like KDE 3.5, have you tried Trinity?