[Heathkit] Hum in SB-401?

[OTAKEBI at aol.com]

Hello to all with a question.
Have an SB-401 that seems to have a new problem.
A station I was talking to last night says that he hears hum in SSB  audio.
Voice is not distorted but hum can be heard.
I dead keyed the mic and hum was in signal.
I shorted mic connector on rig w/o mic and other station could still hear  
hum.
I can not see it on my scope but I do hear a hum in the transformer  area.
and it gets more pronounced in CW keydown.
No load I am at 400 on meter as I should be and with load I drop down to  
about 380.
I am getting full output as far as RF is concerned and good clear  audio.
Any ideas other than caps in power supply going bad?
Could it be the transformer or do they all make noise?
Thanks in advance.
Dan/N4VET