oxygen sensor question

Hey all, I need to get a new oxygen sensor and I had a couple of questions. When I look up the part number it askes me if I need a single wire, double wire, or a triple wire. I just wanted to know what this meant. I have a 99 1500 2wd rgular cab with a 4.8. Also Ineed the sensor that is located right beneth the driverside door jusy past the honeycomb. So what would that sesor be called. Thanks for all the help.

What code do you have, that will tell which one you need to replace, there could be 4 on your truck, should be 4 wire type, but look to make sure.

Well, I dont have a code or anything. Heres the deal. I thought my cat was going bad because when I first statr my truck and everytime I press the accelerator I hear a loud rattling noise. So I went to get my cat fixed and the guy wanted to know what type it was. So he lifted it up and he started to bang on the pipe just behind the honeycomb and he thought the honeycomb was breaking up. Well he took out the oxygen sensor and banged on the pipe again and the rattling was gone. Then he shook the oxygen sensor and it rattled. So he put it back in and hit the pipe and the rattling was back. So to get rid of the rattlig I have to get a new Oxygen sensor. But the thing is that their is no code or any check engine light. But I have noticed that it is idle kind of rough but not to bad. But yeah, have you ever heard of that before. So any input at all is gladdly accepted. I thought maybe wrapping some tape or something around it to balance it out to stop it from rattling but Im not sure if it work. But thanks for the info earlier.