On the front page Sound Design there is the area 51 link (on the right side) which after clicking shows Page Not Found on Area 51 site. I am not even able to find the Sound Design site on Area 51 (searching keyword "sound"). Why does this happen? Was the Sound Design site substantially renamed?
Sound Design was never an Area 51 proposal.
It was a Stack Exchange 1.0 site (Social Sound Design) which was recently migrated to the Stack Exchange 2.0 platform (some of the content of the original site is in Sound Design, some into Audio Video Production).
The code assumes an area 51 proposal for sites in beta, hence the link. However, since it didn't have a proposal, that link is dead.
As a very rare occurrence and since there are no more Stack Exchange 1.0 sites to be migrated, I am declining a fix.
While we won't be able to set up an Area 51 page 'proper' for sound, since no proposal existed for it, we will be making sure that the broken link and display stops showing. A change was made that should take affect in about an hour to no longer display the Area 51 links.
I'm leaving this 'declined' because we can't make it look like the rest of the sites, but we have fixed the immediate breakage.