Yes, I am using a G4 Mac keyboard, with volume control buttons. When I press the volume up or down keys, the graphic appears, showing me that the volume is allegedly going up and down, however the volume remains the same.
Hmmm... that's strange. Is it the internal speaker that's doing this, or do you have a set of external speakers connected? Can you try with different sets of speakers, no speakers, etc. and see if the results are different?