As I googled it, seems like I'm not the only one who can't tolerate sound of running belts. So now you can just mute them entirely. Tested with Bob's Logistics belts, but should work fine with any others since it just run through all collection of data.raw["transport-belt"]. Please report any issues in forum topic or PM me on reddit.

Previous versions of "Silent Belts" 1 and 2 by GotLag and Alan respectively that I found are obsolete and seems like not supported anymore, so I thought to make my own. Also that mods supported vanilla belts only, while this one affect all belt types.

In future I want to find more pleasant and relaxing sounds for belts and introduce them in another mod so you would rather find an opportunity to stand near them and just hear it. But by now I think this should be fine temporary solution for suffering engineers. That sound is still playing in my head when I stand near belts, but my ears feel actual relief and I don't feel like I need to run away into the forest anymore. Hope you will feel the same :)

Changelog:
v1.0.0 - 29.11.2018 - Initial release