From: The The Best of the Hollow Hassle - (Vol. 5, No. 4 - Aug. 1984):

Dear Mary,

"...The number of caves here is incredible! We often hear strange rumblings and something like machinery (underground), a kind of low roar. A lot of times our TV set picks up this noise. Don't know what it is."

Best Wishes,
Persephone - Little Joe, Arkansas