This is a fun one. I am slowly leaning towards my GPU might be dying but I would like some expert insight.
 
Every now and then my computer will start micro-stuttering. It stutters almost every 300-500ms exact. Mouse movements, key strokes, windows dragging, all that stuff freezes for a brief moment then jumps to where it should be. Audio never lags out. It occurs most frequently when I launch NZXT Cam or when playing PSO2. When it occurs in PSO2 it almost always begins right after a load screen. I have never had this occur in any other game or software. When it occurs, rebooting does not solve the issue. I just have to wait it out then it disappears on its own. Someone told me maybe something is triggering windows memory diagnostic and its running in the background, but I have disabled those tasks and can't find the service anywhere when this happens. 
 
https://www.youtube.com/watch?v=6PVPVGcE-Rc This is a video I took with the game still running in the background. However, this is exactly the stuttering that continues even with the game closed and after reboot. 
 
I have reinstalled windows. Tried Windows 1909 and 2004. Tried multiple nvidia drivers. The problem never happens if I use my onboard video. I have troubleshot a lot over the past few days and what I have discovered is below. 
 
My specs are:

• Windows 10 Pro x64
• Aorus Master z390
• i7 9900k @5.0GHz
• 4x8GB Gskill Trident @ 3600MHz
• EVGA 980ti
• NZXT Cam and EVGA Precision X1 for monitoring/cooling software

When the stuttering occurs there are 3 threads that get pinned higher than dxgmms2.sys when inspecting System -> Threads with process explorer. ntoskrnl.exe!KeRaiseIrqlToDpcLevel. The issue is they never resolve once the stuttering begins. 
 
I did an xperf with no game running and attached (xperf.png) a lovely little 20s blurb of spikes. Each spike is utilizing 100% of a core. However, it happens so fast task manager never picks it up. Task manager only says ~5% of CPU is being used. If you zoom in on a spike you get to see (zoomed-in-spike.png) that the spikes consist of 2 stacks, nvlddmkm.sys and ntoskrnl.exe. One is the nvidia driver and the other is windows kernel. The driver is firing off 35x more than the kernel based on the count, so I am leaning more towards driver issue. That is why I tried different drivers and whatnot. 
 
Using latencymon (latencymon2.png) there are a lot of DPC counts for the nvidia driver and an equal number for the kernel and wdf01000.sys. No idea if this means anything. I know enough to be dangerous but not enough to make decisions for myself.
 
So something is causing the kernel and the driver to fight each other I guess. And since this build is less than a month old, minus the GPU, I am leaning to the GPU is dying. Sadly, I don't have a spare to test with, nor do I want to buy a new one since the 3xxx series is coming out later this year. Buying now I would be outside of the step up window :(. Any insight would be insanely helpful! I have posted this similar issue to the Nvidia boards with 0 traction. Just someone telling me my system is fine.

I have tried using stock settings with xmp off and it still occurred. I have not tried a different PCIe slot and will set that up now. 

Do you have another pc you can test the video card in to see if the issue will follow the card to another pc?

Well then you could always take the card to a local pc shop to see if they can reproduce the issue.

Someone just informed me it could be the EVGA Nu nahimic driver causing issues and linked me to this post. https://www.reddit.com/r/MSILaptops/comments/7uucrb/everything_nahimic_2_possible_fix/ Old, and not EVGA Nu dirctly related, but does talk about the nahimic itself can be a PITA.  

Sad to say uninstall Nahimic did not solve the problem :(

Completely removed the Nu card and removed all drivers and references to it. Testing from here. Will post with updates.

I am down to just my GPU, mobo, and RAM hardware wise. Driver wise just basic motherboard, nvidia, and networking stuff. Completely nuked ALL audio drivers. Problem still exists. :( I contacted EVGA support to see what my options are regarding the situation. 

A friend had a 650TI that he is letting me borrow. The stuttering issue went away.
 
Now I am just haunted by the pinned threads that appear every now and then related to the nvlddmkm.sys and DPC's. No one seems to be able to give a reason why that occurs for ~30 minutes. Probably just some weird Windows bug with the 1909 & 2004 update. 

Solution (Hopefully):
TLDR of Problem & Solution:

1. Sometimes - 3x "ntoskrnle.exe!KeRaiseIrqltoDPCLevel" threads pinned to System higher than anything else.
   1. Found with Process Explorer
2. Only if #1 - nvlddmkm.sys had a .3s window where it would use some or lot a core. This happened at a consistent interval.
   1. Found with 'xperf -on PROC_THREAD+LOADER+PROFILE+DPC+INTERRUPT+DRIVERS -stackwalk profile'
3. If 1 and 2 existed at same time, 980TI would stutter every time #2 showed up.
4. If 1 and 2 existed at same time, 650TI would not stutter.
5. Problem existed in Windows 1909 and 2004 with NVIDIA Driver 446.14, 442.74, and 418.91.
6. Upgrading to Beta Driver 27.21.14.5099 caused #1 and #2 to go away.

Personal uninformed rationale of what was happening:
 
At some point the Windows kernel is trying to do an interrupt involving the NVIDIA driver. It doesn't receive a response it likes, so it sends another interrupt, and another. This is why there are 3x pinned ntoskrnle.exe!KeRaiseIrqltoDPCLevel. What it is trying to do involes the nvidia driver, nvlddmkm.sys. The driver will keep repeating itself, over and over, and eventually fix itself. This can be seen by the .3s long spike, flatline, then finish via the xperf zoomed in picture (ASCII ART start /------\ finish).
 
While testing, the problem exists in Windows 10 1909 and 2004. However, in Windows 10 2004, they claimed they fixed a problem with NVIDIA Multi Monitor refresh rate. Okay cool, so something changed with how Windows and NVIDIA interract. However, the problem did not go away with 2004 as mentioned before. BUT there is a Beta NVIDIA driver that adds some extra fixes for 2004 update. I installed that and tested everything with the 650TI. It seemed fine, but I noticed #1 and #2 was NEVER happening. Whereas before the beta driver, it would happen multiple times a day, lasting 30+ minutes at a time. Starting NZXT Cam, Spotify, or gaming would force the problem to occur.
 
I reinstalled my 980TI to see if I could get the problem to show up, since with the 650TI stuttering never happened, but #1 and #2 still existed. So far #1 and #2 have never shown up with both cards. For now, it seems the solution is to use the NVIDIA Beta Driver 27.21.14.5099 along side Windows 10 2004. Hopefully I am not jinxing myself saying its fixed.