The first thing that stood out to me is that the spawn effect is barely noticeable. First I thought the enemies come out of nowhere...Also, give some time at the end to see the final score :P
And I did not have problems with the sound :)
hmmm I tried to make the spawn effect stick out, I guess I just suck at that lol. Should the particles have been bigger?
Also I thought I added a timer before I restarted the scene but I think I accidentally deleted it :P