Throat clearing is hard to avoid when you have a stubborn spot of thick mucous rattling around and you're trying to sing. Clearing your throat will remove the bothersome mucous but can also irritate the leading edges of the vocal cords. When practicing, try to sing the mucous off. If you must clear your throat, do it gently and avoid habitual throat clearing.
(Note: These guidelines are not intended to be a substitute for professional medical care. Consult your physician if you develop health problems).