A similar type of unexpected large sound, the Seneca Guns or Barisal Guns, has been recorded for centuries. While there is no firm explanation, they are believed to be the result of the atmosphere unexpectedly magnifying loud sounds, such as thunder, ship cannons, or, yes, heavy machinery. While it is not clear how this hypothesis could be tested, most other worldly explanations -- earthquakes, continental shelf movements -- have been ruled out. It is especially notable that these sounds most often happen in summer, and rarely if ever happen in winter.
An important data point comes from Dr. Calvert's essay on the subject:
An apparently different phenomenon was first noticed in 1666, during
an engagement of the English and Dutch fleets in the Channel on 1
June. The sounds of the guns were heard in London, but not on the
South Downs, Deal or Dover, all points between the battle and London.
This was recorded in the diaries of John Evelyn and Samuel Pepys as a
remarkable occurrence, that the winds brought to them the noise of the
guns, but not to the people in between.
So, while there is by no means a firm explanation for this, unexplained loud noises have existed for many centuries, and the atmosphere is known to be a large, anomalous, and complex thing that produces strange sights and noises.