The Allnic units use gold plated tube sockets with gel impregnation. In many older nuvistor products, the sockets would corrode as well as the pins. I think the pins of nuvistors make them much more sensitive to corrosion because of the small sizes. Some of the nuvistors come with very long leads that look like they were intended to be directly soldered, and that may be the best way to assure corrosion free contact and low noise longevity.
As stated, if they get noisy in the Allnic, the tube sockets won't be to blame and my own experience is that cleaning the pins and using a dash of contact enhancer quiets them right down again. I have had the unit for several years now.
The nuvistors right out of the box need to be cleaned and treated before insertion, or are you are going to have some noisy fireworks when plugging them in new.
If was the sockets, why did replacing the nuvistor work? Or why moving the nuvistor in and out of the socket a few times didn't result in the noise going away? So doubt it was the socket.