Never been to that specific site myself, being over in Staffordshire, but the description of the place rings a lot of bells with mills I've investigated here in the UK. Old industrial sites have a very particular atmosphere that's hard to put your finger on - not your classic ghostly manor house vibes at all, something heavier and more oppressive. A lot of researchers think it's connected to the repetitive nature of the work that went on there, decades of the same routines, the same people, possibly the same accidents. Almost like the building holds a kind of psychic residue from all that.
What specifically did you feel? Was it more of a directional thing, like it seemed to come from one part of the building, or more general? I ask because in my experience that distinction matters quite a bit when you're trying to work out whether you're dealing with a location imprint or something more active. Would love to hear more detail from anyone who's actually been inside the place.