A group of friends have started to play the game recently and I made this small list for them, and then I realized maybe it could help other people that are new to the game as well, so I decided to post it here.

Note: Most of these sounds are picked up from the sound hearing distance, which is that circle that forms around your minimap pointer when you run/jump.

• (*1) Sound happens at the START of plant/defuse. Planting/defusing progress is silent. Also there is a different sound on a slightly higher pitch when spike is half-way defused and they start defusing again.
• (*2) Some weapons don't have scoping function and some have "alternate fire" on right click instead (Classic & Bucky).
• (*3) If you have a weapon equipped and you pick one from the ground, you will drop your current one. Also you can drop weapons or spike silently to a teammate if you're close enough and it doesn't hit the ground.
• (*4) Some abilities leave a remanent sound over time, like Sage's heal, Phoenix's fire or Jett floating. Some are also heard while placing them like Killjoy's nanobots. Also Ultimates emit a global "catch phrase" that let's your enemies know who used it.
• (*5) This is also know as "pulling out" a weapon or ability.

And here are some agent specific interactions:

I hope this helps anyone.

EDIT: Thank you everyone for your feeedback, reports and suggestions. ♥