Basically this all started when someone on Outpost Skaro (known for posting various info about Doctor Who and getting it right before) said something is happening on Sunday. Nobody thought much of it. Then, some random person said that at 7pm (GMT) the new Doctor will be announced on BBC One in a half hour special. The fact that it hadn't appeared on our planners was that the BBC was covering it up with Mastermind Repeats.
Nobody thought much of that either, since it was from a random source - until now.
Earlier today Metro posted this article before very quickly removing it:
http://webcache.googleusercontent.com/search?q=cache:http://metro.co.uk/2013/08/01/new-doctor-the-next-doctor-who-lead-actor-to-be-unveiled-this-sunday-on-bbc-one-3908220/ (taken from Google's cache feature).
Now it's come from a reliable source technically.
NOW every other news outlet is saying that we're getting an announcement from the BBC at midnight tonight (which is presumably the announcement of the announcement happening on Sunday).
http://www.radiotimes.com/news/2013-08-01/doctor-who-announcement-imminentNotes: The person on outpost skaro that posted about a Doctor Who thing happening also posted a picture of Paul Mcgann's face, who has been rumoured to play a part in the 50th anniversary episode or even just be doing a mini-sode for them (which could presumably be a regeneration into John Hurt if the current theory is correct). So who really knows?
Also,
Peter Capaldi yesterday had a very large surge of votes in the betting area similar to how Matt Smith did before his announcement. Could this mean he is the new Doctor and we're finally getting an older Doctor?