https://www.cyclingnews.com/news/mechanical-doping-claims-resurface-at-tour-de-france/
Ah there it is
> There is a strange noise. I can hear it while riding. It comes from the rear wheels. A strange metallic noise, like a badly adjusted chain. I've never heard that anywhere," the rider said
> Two days later, the same rider reported back pointing out that the four teams that featured the noises coming from their rear wheel. "Four teams have this little sizzle in the rear wheel," he said.
> Another rider said that talk in the peloton isn't about a motor in the crankset or seat-tube – the most popular rumour that has been circulated about possible mechanical doping in the past decade or so. Instead, he talked of an energy recovery system similar to the technology used in Formula 1 cars. "There is no longer talk of a motor in the crankset or an electromagnet system in the wheel rims, but of a device hidden in the hub," he said. "We are also talking about an energy recuperator via the brakes. The inertia is stored like in Formula 1."
And of course, an old time classic
> A third rider, not quoted in the article, is also reported to have raised concerns about the situation. One of the riders noted the relative strength of the four teams in question, with 13 of the 19 stages so far having been shared among them. Who will dare to speak out? We're not doing anything, and the situation is serious," one of the riders said. "Usually, we have a team that dominates. Or a team that is weaker than the others. That's sport... This year, four teams are far above the rest. The smallest rider who signs with them becomes very strong. If he changes team, he becomes average again. How can you explain that?"