Check engine light is on & clicking noise from engine

I've got a 1999 Mazda 626 that recently started making a clicking noise when I accelerate. My check engine light is on... What is this clicking problem and how much would it cost to fix?

Take your car to an honest mechanic who can check your codes and follow through with the proper troubleshooting. It could be a knock sensor. It could be anything. Pay to get the codes checked out, it's worth the money. That's how I found out I needed an o2 sensors. I didn't have clicking, though.