Does the motherboard use a 7050PV Northbridge ?

According to this, 7050PV supports HDMI, and with it, is the possibility
of sending audio in a digital format, across an HDMI cable. Now, your
motherboard uses a DVI connector, but it could still be, that the
interface is HDMI capable, and that is where your audio went.

http://www.nvidia.com/object/mobo_gpu_tech_specs.html

http://en.wikipedia.org/wiki/Hdmi

Have a look in Windows, "Sound and Multimedia" audio tab,
and see how many audio output devices are listed. There
could be an audio device via HDaudio, the RealTek ALC662
HDaudio codec. But there might also be a digital device listed
which is related to HDMI/DVI from the 7050PV. It could be,
that installing the Nvidia video driver for 7050PV, added
in the digital audio capability across the monitor cable.

You might be able to stop it, by "disabling" the HDMI
audio capability in Device Manager. Or whatever the
equivalent of "Sound and Multimedia" exists in your
control panels. Have a look around, and see what you've
got listed.

Best guess,
   Paul