This mysterious incident happened when I was a kid. Uncle Vilbat, who lived in neighborhood, fell out of a Jack tree while climbing up to pick some fruits and was seriously injured. He passed away after few days as a result of internal bleeding and fractures.
This Jack tree was commonly called "Kos Pandura". Because the tree had several well grown branches spread out of a short stout trunk. Land on which the tree was completely fallow and bushy except some well grown big trees, moreover it was the only Jack tree there.
After few month of his tragic death, people experienced hearing the sound of "drop of Jack fruits" at dusk and dawn some days. That land was located within the immediate vicinity of our backyard, almost at the same distance, there were several houses around this piece of land.
This strange event took place without long interruptions even at times off season for Jack bearing. This puzzle aroused a feeling of fear among us, since we had the ability to understand natural events accurately like drop of fruits, walking of animals and such like, with skills we acquired at childhood. It was heard by everyone including those who were in the neighboring houses at the same time.
As I have heard, some young people had gone several times to look for whether the fruits had dropped around there or not, surprisingly there were no signs of any fruits. The other strange issue was that the incident continued for several years.
Owners of the land cleared the bushes and shrubs over the years, but the sound of dropping stretched as usual. This incident ended when the land was completely used for Rubber cultivation removing all big trees including " Kos Pandura".
I am of the opinion it could be of a more mundane origin like air in pipes, or even natural cause (e.g. The grouse a bird which makes thumping noises). Although a jackfruit is really quite large and makes a unique sound. I do love eating it that's for sure!