Well, not even 6500 miles on my truck and we're replacing an oil pump. Apparently there were a few of these engines built in a certain time period that had faulty oil pumps from the factory. There was a gap between the casing and pump that was basically aerating the oil. This causes an air rush noise on initial start up, and a lifter tick.
Luckily GM put out a bulletin on this issue so we knew exactly what the issue was as soon as the tech heard the noise. I just hope there isn't any long term damage to the internals.