No Sound in Multiplayer on first server

This is a strange one.

When I join a server in Team Fortress 2 there is no sound at all, that
is until I disconnect and reconnect and all sounds work fine. The sound
will then continue to work as normal from server to server.

At first I assumed it was just a bug in TF2, and seeing as pressing
'disconnect' and rejoining the server isn't really a massive
inconvenience to correct the issue, I thought "well they'll probably
iron out the bug in a future update."

But I fired up Crysis Wars earlier, and the same problem occurred:
Joined a server: No Sound
Disconnect, reconnect: Sound as normal.

Strange thing is, I get sound in the menus before I join a server.
Single-player sound in any other game works first time, and I dont get
the problem with GRID/GTA4 online or offline.

Started happening a few weeks ago for no apparent reason, I haven't
changed my hardware or configs, etc. so cant really pinpoint what may be
the problem.

I have 5.1 speakers and a Creative usb external sound card, (the only
reason i use this sound card instead of the onboard one is because i
couldnt get the sub to work with the onboard one - a known problem with
vista)

But nevertheless, all sound works perfectly in all other apps... Just
not FPS multiplayer!?


--
Fast-Eddie