I have a 97 Ranger XLT...sometimes when I turn the ignition I hear a "clicking" sound before the engine will start. It kind of sounds like something is "clicking" into position or something. I was told that it could be a crankshaft sensor. The problem isn't consistent...but seems to be getting more frequent. Any suggestions of what this might be or if it is a crankshaft sensor how big of a job it would be to replace?

Thanks for any help!