David -
It could be something else, but it could be too much sulfite. This
is fairly easy to handle prior to bottling (simplest approach is to
rack a few times, with some good splashing). However, if you have
already bottled this batch, your options are more limited. You could
open all the bottles, pour the contents back into a carboy, and take it
from there (rack and splash) until the sulfite odor is gone, then
re-bottle (with fresh corks). Alternatively, you could do the same
thing when you open a bottle -- open it early, decant it (maybe pour it
back and forth once or twice) and let it sit for a while before
drinking. Time alone is a reasonable option only if you're very
patient -- if the bottles were properly corked, it could be years
before the sulfite level drops significantly. Most of us aren't that
patient. :-)

Doug