Speaker humming from a new Mcintosh MA252

[Berman002]

Hi all, i just found that my ma252 having a humming sound from the speakers, not sure since day 1 or not.
humming sound when you put ur ear right next to the speakers.
both speaker and volume does not affect it.
can any of the expert help please?
I have tested all sort of things that i can test so far, nothing work.
tested:
no input.
different power cable,
different speakers,
different power point,
turn off all the power in the main except the audio power point.
test with 2 pin power plug

the humming still there as long as the speaker is connected and the amp is turned on. it's not affecting my listening, but still ignoring.....
may need to take back to Mc to service.......owned it for 3 months only from new....... any suggestion guys?