I just got an RMA to send my tubed phonostage back for a pesky hum.
Did all the obvious ground connection-lift etc.
Isolated hum to the phonostage output(disconnected input)
Opened up the unit. Followed connections from the jack, noticed some wire touching each other.
Saved myself the hassle and expense and most important-downtime .
Nice and quite now! My unit is full tube-rectifier and active gain. Almost as quiet as a church mouse.
I'll leave diagnostic suggestions to more qualified posters. Likely something simple. Tubed phonostages(even the finest) have some degree of noise. You're just not expected to listen with an ear pressed against the speaker grill. Otherwise, it should be acceptable to most ears.