I bought the 07 in December and it would always start right up and run smooth. The last few starts the truck shakes and knocks after starting and even while driving around you can hear the knock. I was starting it in cold weather before no problem. It sounds bad on a 60 degree day now. After driving for about 20 to 30 minutes the sound goes away and the truck sounds perfect. Also if I put my foot into it the sound will go away but as soon as I let of the throttle and run at a set speed the knock comes back. Sounds really bad when taking off from a stop. What could this be??? I took it to the dealer and they said that if no warning lamps are coming on then it is probably a cold motor. I took it out today and it was running 195 degrees and was still making the sound. Drove the truck around at all different speeds and RPMS and the nosie stayed there until 30 minutes later after going 60 mph I let off and the sound was gone. The truck has 2000 miles and I have really been impressed with the truck up to this point. Did not pull with the truck until it had over 1000 miles and before that I never ran at one set speed or rpm. I let the truck warm up three to four minutes and cool down before shutting off. So what could this be? I have run diesels my whole life and have never heard this before. Thanks for any help. Alan