So in the Weathermod modpack there's a resources folder which has waterfall.ogg in it. I tried renaming it, which caused, when loading my savegame, minecraft to crash. So I tried replacing the default waterfall.ogg with a dummy version which has no sound and that fixed it.
So basically:
1. Open the Weathermod modpack (it should be under Appdata/Roaming/.technic/modpacks/attack-of-the-bteam/mods/Weathermod(version number)
2. Navigate to assets/weathermod/sound
3. Replace waterfall.ogg with a dummy waterfall.ogg (which has no sound) and voila!
You can create a dummy .ogg file by just opening the sound recorder; clicking start and stop after a second and then saving it as waterfall.wma after which you can google a converter and download the .ogg file!
Thanks you guys! This is really so much better!