It says that we will experience up to 8 thumps per day, for 2 weeks. They will be created by a NASA F/A-18 Research Aircraft flying over the gulf.
The letter, addressed to "Dear Resident", goes on to say that we will be compensated $25 per week if we report the time of these thumps.
I'm not usually a sucker for solicitations but this one seems legit.
It's odd though that cash was in the letter.