pulley squeak

At idle, from outside the vehicle, I sometimes think I'm hearing a noise like a squeaking idler pulley from my 6.0. It's tough to be sure because of all the diesel racket.

Is there an idler pulley or two that are known to be short-lived on six-liters?

Is the 6.0 an engine that "just makes that noise," similar to the Chevy 350 whistle?

5 years, 58,000 miles. Original accessory drive belts.