My cat is going out. I live in kansas. I hear a rattling sound when i press the gas and also when it is idling. I want to fix it the easiest way. I dont really want to get fined either, even though im not worried about "global warming"

So what would be the cheapest way to get it fixed and where would you get the parts

 

Check the heat shields - the spot welds have a tendency to break. Before any other recommendations can be made we need truck details.

 

2004 ford f150 lariat 5.4L 4wd automatic

 

My 02 was doing same thing. The rattling came from pieces of the honeycomb inside the cats coming apart. Just put new Magnaflow high flow cats in to go with my true duals set up. Greatly improved flow, power and overall performance. Not cheap but it's hard to skimp on some repairs. The high flow Maggie's were cheaper than others I found. Just a thought. Wish you luck.