On March 30, 2015, a user named “unfavorable semicircle” joined YouTube. Five days later, the user uploaded their first video, planting the seeds of an ongoing mystery.

Titled ♐230511, the four-second video has no audio, and contains just a static brown image with a tiny, blurry hole. Since then, unfavorable semicircle has uploaded around 72,000 videos to the channel, many carrying similar hallmarks as the first: very brief and often silent, though sometimes carrying a few tantalizing clues.

Until early February, unfavorable semicircle was uploading videos at a rate of just over one every 10 minutes. But since February 5, that rate has skyrocketed, increasing to something like three videos each minute—meaning that the channel will surpass 200,000 total videos by the end of March. (Update: YouTube suspended the account on Thursday for “multiple or severe violations of YouTube’s policy against spam, gaming, misleading content, or other Terms of Service violations.”)

The channel might have lived on as yet another weird YouTube curiosity, not unlike Webdriver Torso, an account that was long a source of speculation for users but later revealed to be a channel YouTube used for testing. But encoded in thousands of unfavorable semicircle’s videos is The Voice: unmistakably that of a man, usually speaking a single letter or number, or speaking a string of letters and numbers, each with no apparent connection to each other. Probably first appearing around eight months ago, the voice seemingly comes from some far off digital dystopia, all-knowing but utterly opaque, almost vaguely fascistic. The overall effect, for even those who have seen hundreds of the videos, is disquieting.

“I too find the whole thing quite unsettling,” says Reddit user Jackalackadingdong, who, along with several others, is investigating the videos. “I felt really uneasy listening to this trying to pick out the sequence in the audio.”

The channel has picked up over 57,000 views since it launched, undoubtedly a large part coming from Redditors like Jackalackadingdong. Another Reddit user, KnotNotNaught, posted some of the earliest theories about the channel, noting several things: The average length of each of the videos is five seconds, and they adhere to a few naming conventions. The names of the first several thousand, for example, begin with a symbol (♐) followed by a seemingly random series of digits. Others have purely random names. The last 28,000 videos have started with “BRILL” and are numbered in ascending fashion.

While the vast majority of videos have been four- or five-second clips, there have been several anomalies. One is a 10-second jarring high-pitched squeal. Another video posted in early February contains blurry images coupled with unintelligible digital audio, somehow creating an effect more troubling than usual. Two days in particular were unlike any other: August 10 and 11, when several videos were posted with irregular visual and audio patterns. One was 11 hours of mostly silence. Another video features the voice reciting the alphabet.

Many Redditors think the key to decrypting the videos lies in two of them, titled ♐LOCK and ♐DELOCK. The first, ♐LOCK, was posted in July, while ♐DELOCK followed in December. They are of different lengths and feature different soundtracks, though, of the two, ♐DELOCK is probably the most intriguing, appearing first in a series of brief snippets in late December, before the full version was uploaded on December 28. The channel then went silent for a week. One Redditor compared the voice on ♐DELOCK to a “distant, echoed scream.”

Theories as to the origin of the videos range from the plausible to the absurd. Is it all a game used to recruit “agents for a super-intelligent AI computer that tries to take over the world?” Others have compared the videos to numbers stations. Still others have suggested that the channel is some kind of test, for either YouTube or a third-party user. But that theory doesn’t explain the anomalies, the videos that seem to appear at random and with no warning.

“What exactly does posting an 11 hour picture, as well as a 1 hour, 16 minute and 1 minute version of the exact same picture test?” Reddit user save_the_pigs says in a post. “There’s no audio to check, and if they were checking for the picture quality why make it 11 hours? Brill B is another example, what’s the point of the ‘1000’ description? How does adding a description in any way add to the test?”

A previous Reddit investigation did not turn up much, though that was just two months after unfavorable semicircle began posting, and thousands of videos ago. And if YouTube knows the origins of the channel, they aren’t saying. A spokesperson did not return requests for comment.

Redditors, meanwhile, are busy compiling their own database of the videos, to probe further for patterns. On Sunday, one user asked the group whether someone should tweet at the YouTube developers in hopes of getting an answer. But other users knocked down that idea, suggesting that the account might be suspended or deleted in response. If that happened, Redditors said, they may never know who or what was behind unfavorable semicircle.

“I wouldn’t want to take the risk,” one wrote.