Never been but this is exactly the kind of place I need to add to my list, old industrial sites are basically paranormal gold because of all the residual energy from decades of repetitive human activity baked into the structure.
What are we talking here - shadow figures, disembodied sounds, temperature drops? Because if you're getting all three together that usually points to something a bit more interesting than a standard haunting in my experience. Had something similar at an old factory outside Durham last year and the readings on my K2 meter were going absolutely mental near the old loading bay.
Anyone know the history of the mill? Specifically whether its built near any notable geographical features, rivers, fault lines, that sort of thing. Would love to know if theres a ley line running through that area because that would explain a lot.