Based on your description I’d say it sounds like the input shaft bearing. If that is the case the transmission will have to be taken apart in order to replace it. It is very important to only use Honda fluid in a Honda transmission so if you do have that repair done, be sure that Honda fluid is installed in order to ensure the repair will last. More info on these issues here.
http://www.ericthecarguy.com/faq/solving-transmission-problems
Good luck and keep us posted.