After I tried ANYTHING for months, including power management and registry tweaks, the only thing that ACTUALLY SOLVED the issue for me (at least -99%) was uninstalling completely "Intel RST" (remember first to force in Device Manager manual installation of Windows std drivers under "IDE ATA/ATAPI Controllers" and then uninstall Intel RST or you might experience a bluescreen "INACCESSIBLE_BOOT_DEVICE" on next reboot).
I suspect Intel RST drivers trigger a too aggressive power saving state on Intel chipset that as a side effect cause those annoying random crackling sounds with Realtek HD.
Running without cracklings since 2 months ago and never returned.
Windows 10x 14393.693
P.S.
Before you ask: no, even with very latest Intel RST from station-drivers site you'll still have random crackling sounds. The only way is to uninstall them completely, trust me.
--
ASUS ROG Strix GL703GS, GTX 1070 8GB, 32GB RAM, 1920x1080 144Hz G-Sync laptop screen, external monitor UWQHD 3440x1440 Mi Monitor, NVMe 4x, 8BitDo Arcade Stick, EasySMX X10 controller, ROG Strix Carry mouse