Nice work. I played the game until the very end and really enjoyed it. The white noise being the call to summon the undead will haunt me for a while, especially since I used to listen to white noise for relaxation, LOL.
The game could use some progression elements, such as upgrades for the turrets themselves. It would also benefit from some visual feedback, especially when placing turrets. You could add a highlight effect like what is usually done in tower defense games. I was really happy that you added the speed up button; it enhanced the experience tenfold.
Question: did you use Time.timeScale to speed up the game, or did you use another method?
Great work.