Question New build unstable only after boot

[framebait]

I build this new pc and it keeps on doing weird things while booting or shortly after. It began with graphical artifacts that only happened shortly after booting. So naturally i RMA the GPU, but it did not solve the problem. Those pink artifacts are still there sometimes, but the screen can also go black and then dark green and recover. The system also shut down after bios post screen once. Another time it froze shortly after booting and only the mouse was still moving. All this only happens once after booting up and then the system is really stable and performs great. Sometimes there is a crackle in the sound, too. That can happen at any time. I have a suspicion, but wanted to hear other opinions, please.
All drivers and bios are up to date. The PSU seems very stable while gaming or browsing, so i doubt it is causing those problems.

The build:
Msi b450m pro-vdh v2
Ryzen 2600
G.skill aegis 3000 2x8Gb
Sapphire rx580 nitro+
Patriot burst ssd
Be quiet! pure power 600
Windows 10

 

[CountMike]

Try setting ram to 2133MHz ?

 

[framebait]

The Motherboard suppports this ram with 2933mhz and that is what it is set to. I managed to fix the sound after reinstalling windows and drivers, though.
The problem of having a blackscreen/artfifacts shortly after boot remains. There is nothing related to be found in event viewer. So i am assuming it is hardware-related?
This doesn't happen when the pc is still warm or comes from energy safe mode. So i think it could be a broken contact on the motherboard?