strange tick

well lately there has been a strange ticking sound coming from beneath my valve cover (i think its called a valve cover--its the thing that says twin cam 24 valve intercooler turbo on it) I was wondering if anyone knew what this was? Is it a major problem that has to be fixed right away? Is it going to harm my engine? but the way its a 1988 7mgte automatic. Any help is appreciated! thanks!