Build:
GIGABYTE Z390 AORUS PRO (NEW MOBO: Asrock Z390 Phantom Gaming ITX)
i5 9600k (Hyper 212 Evo cooler, temperatures are good)
GTX 970 (SECOND TEST GPU: GTX 770)
Corsair Vengeance LED 16 GB (2 x 8 GB) DDR4 3000 MHz C15 CMU16GX4M2C3000C15 (OR TEST RAM: Patriot Viper 4 3200Mhz 2 x 8 GB - PV416G320C6K)
Seasonic SSR-850FX GOLD power supply (SECOND TEST PSU: OCZ ModXStream Pro 700W)
SAMSUNG SM951 NVMe drive
SAMSUNG 840 EVO SSD
Alienware AW2518HF (SECOND TEST MONITOR: ASUS VG248QE)
All settings are at stock Optimised Defaults (GPU, CPU and RAM all stock) for diagnostic purposes.




Software things I've tried to no avail:
1. Reinstalling Windows from scratch (I've tried Windows 10 versions: 1511, 1607, 1703, 1709, 1803 and 1809). All Windows installs are kept bloatware free.
2. Not installing any drivers whatsoever.
3. Installing every latest driver possible, on the FIRST time having located drivers from my motherboard manufacturer's website. On the SECOND time after no joy, on a separate fresh install using Snappy Driver Installer Origin to locate the latest drivers available. I’ve also tried an earlier LAN and chipset driver.
4. High performance power plan (this is always the case).
5. NVIDIA driver settings, 'Prefer Maximum Performance' (this is always the case).
6. Different NVIDIA drivers, cleanly installed.
7. Disabling Windows Firewall, disabling Windows Defender, disabling Spectre/Spectre 2/Meltdown mitigations in the OS versions that it is relevant to.
8. Installed Intel chipset drivers & latest LAN drivers.
9. Typically I was letting Windows manage the page file, I've also tried disabling the page file completely.
10. Updating runtime prerequisites such as DirectX.
11. Tweaking Intel Ethernet configuration to disable power management and disabling various techniques (Interrupt Moderation, Offload, Receive Side Scaling etc). Manually setting link speed to correct 1gbps full duplex.

Hardware things I've tried to no avail:
1. Different BIOS versions including the F7a beta (tried both ‘Fast’ & ‘Intact’). Updates I have tried have contained earlier or later CPU microcodes depending on BIOS revision.
2. Downclocking CPU to 3ghz and cache to 2.6ghz
3. Disabling ALL power saving techniques in BIOS (C states, EIST, SpeedShift, Turbo Boost) & disabling other features such as CSM, Platform power management, Virtualisation (VT-d), Integrated Graphics etc. Tried disabling RAM specific features such as Rank Interleaving, Realtime Memory Tweaking etc.
4. Using Integrated graphics – same spikes.
5. Different Graphics Card with cleanly installed drivers.
6. Graphics card housed in different PCI-E slot (I've tried it in every slot including the last PCI-E slot).
7. Disconnecting the fans.
8. Reseating the CPU.
9. Installing OS cleanly on SSD 1 (NVMe) after having disconnected SSD 2 (SATA).
10. Installing OS cleanly on SSD 2 (SATA) after having disconnected SSD 1 (NVMe).
11. Testing with my old power supply.
12. Trying mobile internet as opposed to ethernet cable (in case it was an issue with the LAN drivers/ethernet port).
13. Checking DPC latency using LatencyMon, DPC latency is normal.
14. A different set of DDR4 RAM from a different manufacturer (both RAM kits are on the QVL list).
15. Alternative DIMM slots of A1 & B1.
16. 1 RAM stick installed.
17. Tried different display monitor: tried DVI-D, tried HDMI, tried DisplayPort.