PronunciationHub, or PH, is a YouTube Channel created on the 31st of August, 2011. It has a very different format both graphically and in script to Pronunciation Book, but on the 3rd of August 2013 (Day -51 in the countdown) it uploaded a video in reference to PB:
It could simply be that this channel saw the opportunity of riding PB's fame and made it's own cryptic video, or it could be something else. The red background
How to pronounce September 24th
The video starts with a fast silent graphical countdown from 5
Then shows "Sept 23rd" while the speaker in a very low voice, seemingly out of breath says:
"Time only goes one way, changing the past is not an option"
Then some heavy breathing. And then a dial tone and the noise of a dial-up Internet connection.
Meanwhile the image changes to "Sept 24th"
After the "handshake" is over an explosion is heard and the background turns red, a disconnected dialtone is heard.
After a few seconds a yellow sign background, black letters, rounded corners indicate:
"The New World"
Starting here Sept 25th
The number dialed is 651-5500 (obtained analyzing spectrum and using this for reference)
Looking up this number I see this is the same that is called in this freesound file. But comparing them side by side, they seem to be slightly different (the last number 5 dialed is cut short in the PH video and there are tiny silence gaps at 32.3s, 39.5 and 40.65s, the final part of the handshake is out of sync and is shorter). So I guess they're both dialing the same ISP. Or the sound file could have be edited to avoid having to give CC credit to the freesound uploader. The freesound is tagged as AOL, so maybe someone can use this, and this site: http://access.web.aol.com/accessnum/ to determine the location of the caller. (Neither Milwaukee or Queens, as in Thomas Bender's area code give the right number).
Other oddities of the channel:
Justin Bieber video includes a scream (possibly mimicking a fan).