Slight hum in my amp. Is this normal?

My amp has been at the shop since Wednesday and the owner called me this morning at 7:00 am when the shop was dead quiet. Said he did agree the transformer on the right was a bit louder than the left however it was a normal hum. 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. Another thing is this whole thing only began when I moved into this house with knob & wire electrical. It is on a 20 amp circuit.
All of these things suggest DC in the line. Just to review; all of the problems began when I moved in this house. First thing was the surround right channel was dead. The shop found no malfunction indicating a loose connection that suddenly worked when I delivered it to the shop. As a precautionary measure, they disassembled it reseated everything. When I brought it home is when I noticed the hum. After bringing it back to the shop, being told it was normal, brought it home and noticed it running warmer than normal and of course the hum was still there. Since I refuse to accept that its operating normally, its back to the shop.
Again with everything I've read, this smells of DC. Even a Torus TOT MAX made no difference. I just ordered an Emotiva CMX-2. I plan to call the shop tomorrow for status.
Anyone care to guess what the problem is?
My guess is; 1- there's a bad connection, 2- a faulty component (transformer), or 3- DC in the line.

There are two issues being discussed in this thread:  the original issue of a transformer hum and hum coming out of speakers.  They are two separate issues.  The transformer hum is mechanical, the speaker hum is electrical.  Hum out of the speakers is caused by one or more ground loops in the system.
Mechanical hum is caused by other issues, typically:  a DC offset in the AC line; electrical noise in the AC line; a poorly designed or implemented transformer; or an old transformer. 
I have three essentially identical amps that are about 25 years old.  The transformers in them did not hum, at least audibly, when they were new.  Now I can hear them from across the room.  Everything I read indicated that since the noise was constant and occurred with no fluorescent lights on and no motors running that it was caused by DC on the AC line.  As it happens, I built these amps at a company I used to own.  I consulted with my ex-partner, the design engineer and he said he doubted there was DC on the line and that the transformers, which are toroidal, were probably just old and the windings had loosened slightly.  I decided to build a DC blocker anyway.  It didn't help.  I tried an isolation transformer.  It didn't help.  I then built a fixture to measure any DC offset on the line.  What do you know, it was zero.
In the end, I moved the amps to the room behind the front listening room wall.  All's quiet on the listening room front.
oldschool1 - I suspect the right transformer in your amp is humming louder because the bias on the right channel is slightly higher.

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