http://en.wikipedia.org/wiki/Scientific_pitch_notation
(toward the bottom of the page).
Even at normal-seeming levels, you -should- be getting a breeze from the
port over at least a few note range (and the cone should almost stop moving).
Even a small leak can whistle at the resonant frequency though... I had an
un-tightened screw blow out of an L19 I was assembling with a test
tone running (just for grins). From that one screw hole, you could feel
the air pulsing out from ~ a foot away.
If there's a leak to fix, it shouldn't be hard to locate.
If the other cabinet is not doing the same thing, and you've traded
speaker wires L<->R (or are using a mono signal), then I'd look further
into the problem.