This talk seems to occur periodically, but this time almost totally outside Japan.
Several US websites have the scary articles, which read more or less "Confirmed: Reactor 4 is sinking unevenly, entire building to tilt".
You can follow the link below (just one example) to learn all about it:
From an article at Prison Planet,
To Washington's Blog, then
To Enenews who quotes Mr. Arnie Gunderson, who quotes Former Japanese diplomat Mr. Mitsuhei Murata, who quotes Mr. Mitsuyo Matsuda, a former secretary of Prime Minister Naoto Kan who quotes an anonymous "high ranking official in the nuclear security agency".
Mr. Mitsuyo Matsuda was a secretary of Mr. Kan before he became the prime minister and before the Democratic Party of Japan became the ruling party. If the source of information for these sites above is ultimately Mr. Matsuda, they may have some credibility issues, from what I've seen. He seems to be famous for his fantastic stories. (About Mr. Matsuda, see this togetter's comment section, if you read Japanese.)
I remember Mr. Matsuda from an interview done by independent journalist Yasumi Iwakami; I was rather taken aback with his assertions about Fukushima I Nuke Plant without anything to back them up. I was also surprised at Mr. Iwakami, for not questioning his assertions.
Mr. Matsuda claims in this interview in June this year (by 8bitnews, set up by former NHK news caster Jun Hori) that Reactor 4 had a core melt (never mind that there was no fuel in the reactor pressure vessel at that time) that resulted in an "elephant's foot" like Chernobyl. He says "it's immediately apparent" if you look at the photo of Reactor 4.