I ran into the same thing. In my case it was poor contacts due to loose pin to socket contact. I would also check if the tube pins are clean.
I rolled tubes and I got hum
I just rolled the two 12AU7 tubes in my Bottlehead II pre with a pair of suppose NOS Telefunkens and right away I heard some noise (hum) coming out from the speakers. The hum can be heard at a distance of about one foot from the speakers, is not very loud and does not increases by turning up the volume. Any idea about what´s going on? With the others tubes (Electroharmonix) the speakers (i.e. the pre) was dead silent.