My '03 does the same thing.
I seem to recall reading that it's pretty much a normal thing, for these trucks. Never had a vehicle that did that, before.
Mine does it only if you turn off the AC, and park the truck. When you restart the truck and then turn on the AC, that's when it happens. If you leave the AC on when you shut the engine off & then restart the truck, it does not seem to do it.
Maybe there is some sort of head preasure that builds up that the AC has to overcome.
Joe F. (Buffalo)