random rebooting & freezing

[Sneupi]

PC randomly freezing and/or randomly rebooting. Happens regardless of pc load. Occurred 3-5 times per week in summer. Now it's every other boot up. Sometimes audio will crackle or video will stutter beforehand. Seems more common after startup (first 15-ish minutes) and less likely hours & hours into pc use.

 

specs:

• Windows 10 Home 64-bit
• AMD Ryzen 5 3600 (3.6 GHz 6-Core)
• MSI B450 Tomahawk MAX Motherboard (ATX AM4)
• GSkill Ripjaws V 16 GB RAM (2 x 8 GB) (DDR4-3600 CL16) 
• Sabrent Rocket (boot drive) (512 GB) (M.2-2280 NVME) 
• Crucial MX500 (2nd SSD) (1 TB)
• EVGA GeForce GTX 1070 SC (8 GB)
• Corsair RMx 650 W (80+ Gold Certified) (2018)

all parts bought new (except GPU), nothing overclocked

 

what I've tried (in order):

• reverting gpu drivers, updating gpu drivers
• ran CPU-Z to test heat (Maxed at 70 C, idles at 45-55 C)
• completely reinstalled windows (via windows10 settings)
• unplug/replugged ram & gpu
• ran memtest ("mdsched.exe" in cmd) (No memory issues detected)