Humming coming from the amp head, not fan, and not speaker.

i just got a eden wt-500 in hte mail that i scored off ebay for pretty cheap. the amp sounds great with a real warm and punchy sound to it. The only issue ive found so far is that there is a low humming coming rom the amp. I opened up the amp and looked inside and the hum is not coming from the fan because the fan is off at low temperatures. It seemes to be coming from what i think are the transformers. The sound is not coming through the speakers either i tried the amp unpluged from the rest of my rig. Anyways i was wondering if anyone else has had this issue and if its fixable/serious. I can definitly live with it because it is no louder than the fan in my old hartke amp but it would be nice if it was silent.

All answers appreciated
Thanks
Ben

 

I correct my previous statment, there is actually a pretty faint hum coming through the speakers but is only audiable when volume is turned up

 

are "Singing transformers" bad and will they cause any harm in the longrun?