I have had this problem of having to clear my throat for years. I have even experienced weird hiccups that would go on for an hour where acid would come up and I couldnt swallow. sometimes I would force myself to throw up which would relax the muscle causing the hiccups to stop. Eventually I was diagnosed with Acid Reflux where Nexium ( expensive) and Prilosec ( inexpensive ) relieved the problem. I found the only way I could control the annoying nasal drip which I believe was causing my clearing of my throat was to avoid dairy products and those items that caused my nose to run mucus,  possibly even allergins.
In my case, after I would eat pizza ( tomato creates acid, cheese is fatty) or ice cream ( dairy) , later that day and the next day I had to clear my throat. Also when it was about to rain ( humidity stimulates the sinuses) , my sinuses would act up causing me to have to clear my throat. I'm sure everyone that experiences clearing of ones throat can remember specific situations or foods that bring it on. Just avoid them and you will experience fewer attacks. 
Hope I have been helpful.