I have an ASUS M3N78-EM motherboard and the problem is that there is no sound when the nvidia driver is in use. The sound works if nv driver is used or, if nvidia driver is in use and ubuntu has been booted with acpi=no option.
When playing something in totem, the pulseaudio volume meters works, and is possible to see it showing sound but nothing sounds in the speakers. When going to a console (control+alt+1 for example) the sound starts to sound in the speakers and when returning to the x display a little noise sounds and the application playing the sound is automatically close, totem in this case. The little noise sound always just when entering in the x display, with nvidia driver and acpi on.
The problem is not only with the integrated sound, also with another dedicated sound card happens, no sound at all. The integrated one appears in gnome-mixer as alc1200 and the dedicated one is a pci X-Fi Xtreme Audio (yes its a X-FI one but it works because is the only X-Fi with a ca0106 chip, is more an audigy than a x-fi).
I have tried also installing 185 version driver from nvidia but the problem continues.
I forget to mention that I have tested aldo enabling msi interrupts in the nvidia module and in the snd-hda-intel module (alc1200 sound card), but that didn't solve the problem.