From the website which Kammer links to below:
..a somewhat spooky story I unearthed about Cholesbury Camp a while back. Ever heard of the ‘Screaming Pigs of Cholesbury’? Well the story is told of strange ‘unearthly noises’ emanating from Camp and the reluctance of even the most fearless of the men of the village to enter the Hillfort after dusk. So if anyone fancying a stroll as darkness falls is welcome to test out this theory let me know what happens!