More than likely it's just the shaders compiling in the background, usually settles down after 10mins or so, although think Gearbox advise it can take up to 30mins. Saying that you might want to consider increasing your shader cache from default to 100GB, BL4 uses around 10GB overtime. Otherwise enjoy you're new PC.
i have read i need to increase the cache in Nvidia app? can i do it without the app? as ive just removed it