This might not be helpful, but I've had issues like this before where troubleshooting the problem didn't lead to any positive results. In those cases I simply formatted and reinstalled the OS to fix the issue.

Some people might consider that an extreme solution, but in reality most personal PC's should be formatted every so often, just backup anything important on an external drive or something.

Shame you don't have integrated graphics. I'd say try running it with a different GPU for a bit and see what happens.

Could be an early sign of SSD failure. This also happened to me, albeit on a mac, so trying the other disk may help.

Have you run a memory stress test?

That seems to be the missing item in your initial list above.

get memtest on a boot device and run it do the full suite. Yes it takes a while and is a PITA because of it.

Well, looks like you've covered most of the basics.

Systems can hang like that when they are awaiting data. If there is a bottle neck somewhere, or a delay - network packets, etc, that can create the symptoms you've described.

What I would do next is fire up the task manager and the resource monitor, and monitor what all of the software is doing behind the scenes. Watch for programs using up resources, or where the system is busy. What is it doing exactly when the glitches occur?

In my experience, it is often either windows, or some third party program, that is hogging resources behind the scenes.

If you can spot it in the act, then you can either remove the program, or alternatively, change it's priority, to change how the resources are being used. For example, my windows system likes to catalog and prioritize all of the files I am using so as to boot the system faster. Indexing - which does boot the system faster, however, the process of indexing is constantly hogging resources which interferes in overall performance.

So - what to do about it? I could lower the priority, to slow the indexing and reduce it's resource usage at any given time, or I could increase it's priority to get the indexing task finished faster, then releasing those resources. Currently I am going with the increased priority, which seems to work better.

Check for maintenance software - especially anti malware or anti virus software, running scans in the background.

Windows loves to scan files like I don't need the resources or something.

Monitor the network traffic too - the problem could be external - delays in network traffic - keep an eye on packet loss and packet latency, or third party programs using the network behind the scenes - maybe someone else using your bandwidth - that sort of thing. Anything that causes the system to wait for data.

Also - random is almost always not random, but has the appearance of random.

It it is heat related hardware failure - then it is likely the problem will get worse over time until the involved component ultimately fails.

Your system is old enough that some transistor or another could now be developing a heat related failure.

Watch to see how long after you start your system from a cold start for the first glitch to occur - record the time.

Also record the time between glitches while the system is operational at full heat, (full expansion.) Watch to see if the rate of glitching is increasing over time. If it is then likely one component is about to fail.

Try to see which components are involved at the time of the glitches. When the hard drives are spinning, when the sound card is in use, that sort of thing. - You may spot a pattern there too.

Sounds like an IO bottleneck is happening. Thats why it only happens for a second. Maybe an old school fix is needed.

In Windows services make sure "prefetch" and/or "superfetch" is disabled.

Go into computer settings, go to advanced and change your page file to 0 both min and max. You have more than enough RAM.

Restart your PC and see if that helps

Thanks for the advice all. I have a good number of things to go back and check/test!

Probably hardware issue. Check your device manager for issues there. Try to first roll back video card driver to an earlier version.

Swap video card out for a known working one and install it's drivers, then see if it's still happening. If it is, remove everything from the motherboard except CPU, one ram stick, and video card. If still happening, motherboard might have taken a shit.

Try the components from the bad PC in a known good PC as well if still stumped after all of that, just to prove they aren't the cause.

Did you run task manager to see if there is anything at 100% hdd cpu mem? Also look there for a process that’s hogging resources.