“Illegal miners get their hands on some surprisingly niche tech” seems many many orders of magnitude more likely than anything related to aliens.
Would be interesting to corroborate whether unusual noises are associated with their arrival.
Not to say that "aliens" is necessarily less far-fetched... but it's up there for sure.
Money motivates+enables narco-traffickers to acquire some pretty amaze-level tech. So why not miners too ?
Would illegal miners even have access to jetpacks?
That is also the title of a pretty funny movie.
Sound doesn’t reflects well of water so if you can easily mask it by flying close to the water and quickly jumping over.
I probably couldn't do that for the full 10 minute flight time though.
It is not some bootleg mining to scrape by.