I'd bet on an instrumentation problem ...
That's what I was wondering.
4) one of the main signals that these guys see is an annual variation. Annual variations can have any number of alternative explanations.
Yes. I read a story (which I would be grateful if anyone could track down for me, I've tried and failed) about a group of scientists in, I think, Germany, who thought they'd found an annual variation in the gravitational constant.
It turned out their university had a large coal cellar which was filled up at the start of every winter ...