Hopefully you find something that helps, I too have this problem It ends up being constant I don't always conciously notice but excess ends up in my lungs and I have to cough it up and I am young fit and healthy and people at my work when I start coughing up mucus and *almost that cat sound hairball coughing up sound, but a few levels less in severity* say things like "My grandpa doesn't even sound as sick as you"
Basically i've taken measures as to cut out Sugar for months, drink grean tea every day and keep hydrated .. no caffeine apart from tea.. and the only milk I consume is soy milk occasionally but it is still constant.
This may help from researching about this I still havnt fixed myself but another term for this is;
'Catarrh' to be more narrowed down entirely to the mucous problem might help to search into that info aswell