I Have This Constant Musty Smoke Smell In My Nose

I have this constant musty smoke smell in my nose that is very annoying..when it first started it was just every once and a while and would come and go....now it's constant. had an MRI with contrast of my head and sinuses everything came back as normal. I've been to an ENT several times and they've found nothing that would be causing it....no infectin or polyps of any kind. Sometime I seem to notice it more right after I've eaten or right before having to use the bathroom. It's gotten to the point now we're the smell sometimes makes me feel not feel well