You can play sounds and give them tags. Like this, you can also check if a sound with a given tag is playing or in your case, isn't playing.
-> On object clicked (or on drag start if it's drag & drop behavior)
X Is "sound" playing (inverted condition, so is "sound" not playing)
: Play "mysound" with tag "sound".
Tip: you can invert conditions either with right click - > Invert or use the keyboard shortcut "i".