So about 6 months ago my truck, '03 Crew Cab Long Bed 4x4 v-6 (about 160k miles), developed a rattle on start up. I started researching here and other places and figured it was the lifter rattle that is frequently mentioned. It wasn't too bad, so I didn't worry much about it. About a month ago it started getting much worse. It sounded like a death rattle, but after it stopped the engine sounded completely normal. I did determine that the sound was coming from the bottom end by raising the hood and starting it from outside and quickly going to the front and listening. That made me feel even worse. Then I took off the skid plate to change the oil and had my wife start the truck while I was looking under it. It was the crankshaft pulley also known as the harmonic balancer. The rear third was flopping around a bit until the noise stopped and then it looked normal. After I was armed with my new knowledge I did find just a couple hints that poeple had had similar problems, but it was never associated with a startup rattle. So, I thought I would post this here to help someone else possibly find a problem with their truck. So I changed out the pulley today and the rubber was completely broken, it came off in two pieces. Anyway I hope this helps someone sometime.