Quick info for everyone wondering why they're still not hearing weapon sounds:

We changed the way the server sends sounds to the client.
The client now ignores the old "piggy-backed" way of sending weapon sounds in order to prevent double sounds.
Servers that aren't updated yet will not send sounds in the new way, yet, which results in not being able to hear sounds at all.

So if it happens to you, find another server that is updated (see the list on the previous announcement).