If the GPU runs after heavy GPU usage at 1500RPM I simply 'sleep and wake' my system resulting the fans become idle again. Without GPU load it runs perfectly (some coil whine indeed). After heavy GPU use it doesn't spin the fans to idle (0 RPM)anymore. There is one issue which remains with the card. I'm following this thread a while and my outcome is that my Sapphire RX Vega 64 Nitro runs best without a PowerPlayTable (Mojave). I'll try to put together a more detailed comparisson, including Gfxclk_Table and PowerTune_Table. However, I'm checking table versions and PPT versions of some of the problem and fixed bios and I'm only finding PPT version: ucTableFormatRevision 8, ucTableContentRevision 1, ucTableRevision 0. Graphics clock table also has two versions, the Powertune table even has three versions:

This might explain the behavior, if Apple is not interpreting the table correctly. FanMin and FanMax RPM didn't exist in V1, but exist in V2.

It seems there are two versions of the Fan_Table, in V1 what is now the acoustic limit was a RPM value, the description says it's the default RPM value. In V2 it became acoustic limit, the highest allowable RPM. MacOS on the other hand uses the Throttling RPM value as the Max Fan speed and Accoustic Limit for the Min Fan for some reason. Most Vega cards use Min and Max Fan Speed to control their fan.

Strix vega 64 fans not spinning