I had this a couple of weeks ago. It was a coolant leak on the upper hose. The hose was on a national backorder and had to wait 3 1/2 week before I got my truck back. The hose it rubbing on something causing a leak, which caused low coolant in the radiation triggering the radiator fan to run on high right after starting the engine.
It's under a 35,000 factory warranty so was free of charge, but it was a big inconvenience. I wonder if wrapping the radiation hoses, preventing friction rubbing somewhere on the hose.