filename: rg_hum.wav anyone got sick from that remove it from pak0.pak then you'll be cured
Do you know that modifying stock pak files would prevent you from joining any "pure" server (99,9% of servers), or require you to download the pak file again?
I would suggest, instead, to try creating a file like z_norailhum.pk3, and place a 0 bytes long rg_hum.wav (in the right path) inside it. I haven't tried this, but I think that should allow you do to not hear the hum sound while playing locally, and still allowing you to play on internet servers (hearing the sound in that case).
Instead creating a 0 bytes long file (that I fear may generate some kind of warning in console), I suppose that also a copy of silence.wav renamed to rg_hum.wav could fit.