Eh that depends on how bad it is, I wouldn't keep driving it thats for sure, if it is a lifter it could have been caused from the pistion hitting the lifter meaning you have bad bearrings in your crack shaft and of course it would be getting louder and louder as you drive not just a ticking sound, but of course that is worest last case situation, (happened to me on my last ford) but since you say ticking sound it sounds more like it simply could be the lifter is suck or only opening part way etc... they are tricky I'd take it to a professionl and have them check it out. post back here let us know what it was.