I have an nVidia GPU and I'm using the motherboard's sound chip and I experience the sound bug.
In the first MP game I tried after the latest patch the sound bug appeared within about 2 mintues, it then actually came good again about 5 mins later (yes I held out that long testing other things
)
The next day I flew for maybe 20 minutes, respawned a couple of times and no bug whatsoever.
Both servers were patched to the latest version as well. (I guess they'd have to be as it was the official steam patch
)