How much hum is normal from a new tube amp

I have 3 tube integrated amps , a Line Magnetic 518IA, a Finale Audio 7189Mk2 as part of my main system, and an Ayon Audio Spirit 2 in my second system none of them have ever had any transformer hum

@elliottbnewcombjr  Yes I meant to say KT150, that's what I have.

I have rebiased all the tubes.The hum is present with the preamp off. I used the DB meter from my phone and tracked the loudest reading and it is coming from the back of the amp. I have also changed the power cable, and I just tried plugging it into a different socket. I checked the speaker cables. I have used all this equipment setup with different amps and they are dead silent. 

Normal is none what so ever.

@blue-magoo You could try a DC blocker. Ensure it's on a flat surface. Any loose bolts on the power transformer?

Any loose bolts on the power transformer?

That's the low hanging fruit.  If you press on the transformer, does the hum stop?