I have this issue intermittently on my Surface Book connected via SurfaceDock DisplayPort to an LG Ultrawide Screen which then has the speakers plugged in to it. I have two machine plugged in to the screen, the SB by DisplayPort and the second machine, an HP EliteBook, via HDMI. The HP does not suffer the problem.
The crackling will start at random, no movement of the device, cables, etc. Once it starts disconnecting and reconnecting seems to address the issue, whether that means disconnecting the dock from the Surface Book, or powering off the monitor and back on. It may not happen again for days or it could restart within a few minutes.
No obvious failures record in any of the event logs around the time of the issue.
Running 1809 (17763.134), but has happened across production and pre-release builds.