Fellow Zwifters,
The countdown sound (gong on 2 seconds and 1 second left) while approaching a workout step arc only work if you have started the workout while being in-game using the E key on the keyboard. When you select a workout before joining a world through the game menu, the arc countdown sound is completely missing and silent. Only the sound while riding through the arc is being played.
Having this on my Win10 Laptop, its reproducible every time.