Clicking on any button momentarily raises the sound volume??

That's a new and unexpected one... Am I the only one this is happening to? At first I thought it was only happening when clicking on the "back to tournament" button but actually even clicking on the forum menu provokes this. I'm not talking about lichess sounds here, but the whole computer volume control (I've got music in the background). I'm running up-to-date Firefox on Windows 7.

I often experience the same with my computer, but I never connected it with lichess? I believe that for me it also happens when not on lichess but I'm not a hundred procent sure.