I made a resource pack that should remove the annoying "whoosh" sound effects they added in 1.9 when you're attacking mobs.
The way it works is that it replaces the .ogg files for attacking (located in "assets\minecraft\sound\entity\player\attack", I believe) with 1 sample of silence.
Initially made for myself, I wanted to upload it in case anyone else hated them as much as I do.
The version it currently works on is 1.9.4, but if you need it for 1.13 just change the "2" to "4" value in the pack.mcmeta file with Notepad++. This Wiki page will help.
Anyhow, here you go.
I like mine.