Ok so I tried this several times and it always works for me:

Repro:
Join MM
Tab out and bring ONLY a Media Player Classis Home Cinema window over Dota2's window

So you should have MPCHC's window and in the background Dota2

Effect:
No sound is played when the MM queue is ready

Expected:
We should still hear the sound


The main problem being when in fullscreen on the video, it's impossible to know when the accept window is up.