solid state power amps

Transformer hum. Could be the transformer needs to be tightened. Or could be a design flaw where the transformer vibrates in its mounting or to the chassis.

Or as stated could be that DC has contaminated your AC line.
Is this a low-level hum?

Many threads on here about transformer hum.  Sometimes it's easily cured, sometimes it's impossible however heroic the efforts.

Transformers have no moving parts but they do have alternating magnetic fields due to the alternating AC current and so they can vibrate. Its usually small and silent when the alternations are balanced but even a tiny little bit of DC offset can make enough of a difference to cause it to vibrate to where we can hear it. A lot of DC offset and you need a DC offset eliminator. Or it can be so tiny the tricks oldhvymec suggested will work. Cleaning contacts and all the rest are all great things to do anyway. 

As much fun as it would be to tell you yes this is a solid state thing you need a tube amp sorry, not true. You do need a tube amp but for another reason called sound quality.

It is possible that another device on the same circuit as the amp is causing noise or hum on the amp.  I had this with fluorescent lights and their ballasts.  I changed to new ballasts and the amp became dead silent.  Another source can be lighting dimmer switches.

Can you tell if anything else is on the same circuit?  

Depending on the hum, yes, it could be transformer or ac line noise.  One is cheaper to resolve then the other.   I would call Victor or Steve at BAT. Have them give you some suggestions.
Good Luck!