I have a 5DII, but have never seriously tried using the video capability. This morning, I connected my Sennheiser MKE 400 external mic, then my trusty old Sennheiser HD 25-1 headphones to the A/V out socket, thinking to monitor sound input.
As soon as I pushed in the headphone jack, the LV disappeared from the screen and I heard a loud, low frequency buzz through the cans. The buzz persists even if LV is disengaged and I try to replay a pre-recorded sequence with the mic disconnected.
Am I misunderstanding Audio out, or is the headphone 70 Ω impedence to blame? Is there some sort of work-around? Dumb questions, maybe, but a total newbie at this . . .