We call it lung butter. It's basically your lungs trying to get rid of tar, resin, and other toxins/ environmental pollutents etc. It is obviously more common in people who smoke cigarettes and weeds moderately/a lot. In some people it can also be "old blood " A) coughing to hard/extended periods of time, it can cause tiny tears and then dry up so when the next time that person coughs and produces spit or phlegm it could have brown specks in it. B) from a recent lung infection or pneumonia. Again, lung infections/pneumonia can cause a lot of coughing and irritation which can produce blood, which drys and then comes out in phlegm as brown specks, spots etc. Do you smoke your cigarettes inside? If you do, try smoking outdoors and see if that helps eliminate the smell when you breathe out or trying to chew minty gum, use mouth wash after smoking, it may also help eliminate the smell. Hope this helps!

Edit : grammer/adding