My sources do not reveal whether the voices came from the faery folk or a ghostly spirit, but the fae are said to fiercely protect ancient monuments and sacred stones and punish those who do damage to them. Of course, it could just have been a lazy workman who wanted a good excuse to leave work early.
We went to take a look for ourselves a few weeks back, it's a lovely area and very much worth a visit. We also popped into the nearby Harbottle Castle, and although I've not heard any fairy stories from this location, we discovered a lone hawthorn tree in the centre of the castle ruins that would not look out of place in any fairy story.
Sources and Further Information
Lore and Legends of Northumberland, Jackson Coleman
The Border Country, David Simpson