The last few days I've noticed a "clicking" sound under the hood. My g/f's brother heard this the other day and said it could be the spark plug cables. Should I just replace them?

 

With the engine off visually inspect all of the cables for a worn spot, cracking, or a bulge under the sheath.

Look at the engine run at night, you may be able to see the spark from the cables to where ever it is grounding.

Do not get your hands on the wires, if the insulation has broken down, you will get a shock almost like an electic fence. (no fun).

Good luck