I think there should be an upgrade where you can have the sound of C4 beeping silenced just like the knife where when you upgrade it it's 20% more quieter. So then when it's at max there's no beeping sound at all or there could still be a noise but it's just very quiet, you guys decide (by that I mean @Highwon ).
Eh, they already have the advantage of being able to be placed very sneakily. Being able to kill players en masse silently would make the c4 too OP IMO. It works for the knife because it's a one and done deal.
I wouldn't mind having hilarious custom c4 sounds, but keep the volume. Something like BEEP BEEP MOTHAFUCKA.
Unless I'm about two feet from a C4, I cannot hear it whatsoever - so pretty much I can only hear it when I plant it or disarm it. This could be a problem with my end of things but I know a lot of other players also find it extremely difficult to hear. Having this might make C4 a little bit too overpowered.