Welcome to Healing Well! It is possible that you're getting a small amount of reflux...not enough to create heartburn, but enough to bother your voice, and create some irritation. It's not uncommon for people to have a little reflux after the Nissen.
If you've had it for 6 years, it's possible that things might have loosened up a bit.
Joy's advice is good...talk to your GI doc, and see if he/she recommends some testing to see what's bothering you.