The belt was squealing a bit and the word was “replace the idler and tensioner.” All those parts had been on the engine for 100,000 miles, so for a total $250-300, I replaced everything with Delco OEM original parts from Rock Auto. I discovered that the lower radiator hose had a serious gouge in it, so I’m glad I was thorough about the scope. Well worth $300 and a few hours of my time to avoid sitting on the side of the road with a failed radiator hose! Water pump, thermostat, upper & lower radiator hoses, bypass hose, heater hose, idler and tensioner. And a careful inspection of the radiator.
Also did this front end work a few weeks ago: