Over the last two weeks, residents in South Dakota and California experienced strange mystery booms that shook homes, jiggled windows, and definitely rattled a few nerves.

At 2:00 pm, on November 7th, the residents of the Black Hills area in South Dakota heard a large boom that shook their windows, and vibrated their houses. That very same sound was heard as far as Nebraska and Montana. According to Lane Pilster, a rancher in Alzada, Montana,

The beginning of it was intense, but then faded off with a dull rumbling like a jet was flying by. The sound probably lasted about 8-10 seconds…

According to the Black Hills Pioneer, no seismic activity or meteorological events were reported, and no industrial companies took responsibility for the sound.

Earlier this week, at 2:30 pm on November 15th, residents of San Jose experienced what felt like a minor earthquake with reports of a strange boom sound. However, no earthquake occurred. Susan Garcia, a spokeswoman with the U.S. Geological Survey, stated,

Our duty seismologist did an extensive search and we did not see any seismic activity in the South Bay…So it’s not an earthquake, whatever they’re feeling — as far as we can tell.

Residents reported that wine glasses clinked and dishes in cupboards rattled as the strange shaking lasted roughly 5 or 6 seconds. The Santa Cruz Police Department received calls concerning a loud boom sound that occurred approximately the same time as the unknown quake. The military has stated that it wasn’t a sonic boom from an aircraft, and local drilling companies are stating they are not responsible for the event.

Speculation of the sources of these mystery booms ranges from natural seismic activity, to secret military supersonic aircraft, to paranormal phenomena, and even the second coming of Jesus Christ. The big question is whether these booms have one causal link, or are these separate phenomena that have multiple sources which simply manifest in a coincidental large boom sound?

In an March 2016 article, Micah Hanks provided some potential, albeit speculative, links between “ghost lights” and the mystery boom phenomenon. In another article from July 2015, he writes about a wave of mystery booms in New Zealand that took place over several nights. Hanks points out that these booms are not new phenomena, and that even famed explorers Lewis and Clark reported hearing “unexplainable artillery” in 1805 as they trekked across America.

If these are natural atmospheric or geological events, then they will eventually be studied and understood. However, with any unknown, the mind does begin to wander. Similar to the UFO phenomenon, is our world dealing with something paranormal? Perhaps booms are heard when Bigfoot manifests from his alternate dimension? Are these sound waves of old battles manifesting from beyond the veil? Are we hearing faster than light vehicles entering our atmosphere? Speculation is always more fun isn’t it?

Much like New Zealand in 2015, the American Midwest and West Coast have experienced similar boom events in the span of a week. Will more mystery booms be heard in the coming days, or is this simply a case of mother nature experiencing coincidence?