a) I can't hear anything without headphones

b) Using headphones: I hear this after Windows 10 starts: http://vocaroo.com/i/s1BlTjodgf15

c) The check in Bios "Perform Quick Audio Check" results in hearing nothing

d) When playing a sound file (like on Youtube) I can hear the content, but with noise

Any suggestions?

PS: It's a freshly installed OS