@Everyone: This is a pretty basic step, but please do not be offended by me suggesting it. Can you verify that the issue remains on the system when using a different/newer cable than the one you are currently using? A lot of times these issues happen in cheaply made 3rd party cables (both display issues as well as audio issues) - so we like to eliminate the possibility.
@AndreasGreiner: Sorry for the delay in response on this. I have been looking into it using multiple systems with/without the AV/R in the loop, and am still having trouble reproducing the issue.
Were you able to create that video showing the issue? Also, can you disable all the other audio sources on your system aside from the display audio, and see if the issue remains afterwards?
@Paar: Please re-install the 3345 driver on your system while the sound is still active. This will allow the latest display audio driver to be installed on your system. You have 3123 right now, but the latest is 3129. Reboot afterwards too.
@Gabriel-Stefanescu: Can you attach a copy of your dxdiag please? (Start -> Run -> dxdiag -> Save All Information)
Thanks!
-Nic