Any way to get PoE sounds a wav files?

I so very much want to change my windows startup sound to a necromancer chanting.

You could try using a program to record it with music turned down/off.

What you can do is extract the giant content.ggpk as follows here http://www.progamercity.net/game-files/2143-info-path-exile-ggpk-resources-2.html#post25152, look for the ogg files you seek and use a free software that converts ogg to wav, such as foobar2000.