i have 2 garmin edge devices, a fenix3 and vector pedals, however i chose the gopro session 4 but still use virb edit to mix in my garmin data.
as of 4.x, exported video has continuous audio crackling. internal/edit playback is clean. exports were fine in 3.6.x
i know gopro files are unsupported or something that garmin doesn't test, but if anyone else can confirm this... perhaps the garmin team can simply look for what changes were made from 3>4 that would affect exported audio.
this issue was present when running macOS 10.11 and 10.12