Slight hum in my amp. Is this normal?

I had the same problem with an Ayre V3 amp. I first built a DC blocker and that did not help so i removed the transformers that were humming and took them to a motor shop. They were dipped in that special winding varnish and when i reinstalled them they were dead quiet. What happens is that one or more loops of wire loosen up and then the magnetics cause the loose wire to vibrate. By locking them all back together it solves the issue.

have experience with this one.  DC is in your line.  It not only can cause hum from the transformer, it can damage it (AND WARRANTY will not cover it) if you use it like this over time.  Bought a DC filter from EMOTIVA,  around $100 as I recall.  works like a champ!!!
SILENCE.   My humble opinion.  a great product for the money

 I was having the same problem a little while ago where my amp started humming. I tried multiple things without success but later I found that the problem was being caused by a potable heater connected somewhere else in the house.

if you ground is not isolated everything that is connected to the house is picked up by some of your components.

in my case that's all it took to get it fixed.

Hope this helps.

Adalberto

I have a modwright integrated KWI-200 that developed a hum that got louder over time. I finally had to send it to them and they replaced the transformer.
if this is a new problem since you moved, I don't believe in coincidences. 

I explained again that it was loudest when you first power it up then the hum diminishes after a few seconds but is still audible. He wants to keep power applied to it and observe.
Another thing I just remembered and haven't mentioned, since the hum began, it has been running a bit warm even at low listening levels when it was in my system.

Its 100% normal for any toroid to make a bit of noise on startup. This is because the core of the transformer can become magnetized when the unit is turned off. The next time its turned on, the magnetic field causes saturation in the core and the transformer rattles until the magnetic field is degaussed by the alternating current.

The second paragraph above suggests that the bias of the amplifier is high- which could account for the additional mechanical noise.