It's from the IBS: your mucosal lining. A lot of IBSers experience the mucus. I have some sinus problems too, e.g., sometimes a drainage problem in my throat or excess mucus there. A link to your mucus problems "at both ends" could possibly be one having to do with immune response (body secretes mucus as an immune response to certain stimuli). ? At least, we think that's true in my case (though I don't have much IBS-type mucus).