Brett Manning singing coach to many a star offers this advice:
“Some say that you should never clear your throat, but excess mucous inhibits free vocal cord coordination. The trick is to find a way to clear your throat without irritating it. Do a gentle “whispered cough” (without tone) and then swallow. Repeat. If this doesn’t work, you need to deal with the excess mucous production. Squeeze a 1/4 of a lemon in a tall glass of water and sip over about 20 minutes. This should cut through a lot of the excess mucous.”