Any speech and sound from organics is transmitted telepathically through the astral, so the spirit can hear it; that's how you give a command to a spirit who was lent to you by your Magician friend, for instance; however, electronics are definitely 100% unhearable, and I'm not sure about the others. I guess they wouldn't hear guns and such.
I believe the spirit may possibly be notified of all gunfire, etc by the mage. He doesn't "hear" it and perhaps can't react to it like a normal person (keeping in mind people generally don't use sound to dodge gunshots), but he does know "Alright, so mageguy says lots of guns behind me, gotcha."