Whine with the transmission engaged hot or cold. Sounded like a differential gear at first. Listening very carefully, you can hear it in every gear, up and down but most obvious in 6th at speed. Steady at 50 mph in 6th the whine burbles in and out...de-accelerating much more noticeable than accelerating. Going down or up hill in neutral at any speed, its not there. Clutch in or out standing still, quiet at any rpm. Drove a 2010... nice and quiet. New fluid in the tranny last spring. 24K miles. Input bearing??

 

I don't think it is the input bearing since the noise is not there standing still. This sounds like the differential ring gear whining or a countershaft bearing. It is very common on the Automatic Accord transmissions but can also happen on a MT. It should be still under warranty - what does the Honda dealer say about the noise?