Re: 98 ZJ squeal from engine bay
Depending on how long its already in use, the serpentine belt could have stretched too much or the rubber dried out and cracked. The last is easy to see on the belt inner side. Don't know the engine you have, but for sure it has a belt tensioner. If the belt stretches too far, the tensioner gets to its endstop and the belt tension becomes too low, causing the belt to slip and cause the squealing. If the belt was not changed lately, maybe a good time to do so.
The pulley bearing can become dry after many years of use and make noise as well, but thats normally no squealing. If you don't feel any play on them and they don't make noise when turning them, they should be ok.