I have heard that noise too, and here is how I can reproduce it easily. Leave the truck sitting for several hours. Start the motor and let it run for about 5 seconds, then turn it off. Wait overnight and the next morning start the truck. Presto I get that noise. It lasts a few seconds then goes away and the truck runs a little rough whlie it's making the noise. From what I can tell it's a valve sticking open a little. It would be great if someone else could try this same thing and see if they get the same results.

Damn -6? Geeze I didn't know anything would start in that cold!? Do you use 0w-30 oil? I'm in S. FL so anything under 70F is cold here..