I have a very bad taste when I sneeze and periodically I notice in the back of my mouth. However I brush and rinse my mouth regularly, I don't taste it when I cough. I have been having teeth issues the past few months that has gotten worse and I suspect it may have to do with that. I had a cavity from when I was a kid, a silver one that recently had fallen out so its been exposed it hasn't been hurting but then maybe a couple weeks ago have of the tooth that was supported by the cavity broke off and if down to the gum line, I don't know but I think maybe the tooth and nerve have gotten infected and maybe dying and could be whats causing the taste