cheap belt or bad spring tensioner (if it uses a spring tensioner)

 

Idler pullley. There may be more than 1 tensioner or guide pulley. They have bearings that fail.

 

For the money and eliminating the possibility being broke down somewhere just replace the belt and both pulleys. You'll be set for the next 4-5 years. Belt dressing should not be used on serp belts and it's bad for the bearings in those pulleys.

 

I just learned a new trick for this . A friend who is a moble truck machanic {for 30 + years} put a water pump on his own dodge pick up and the belt started squeeling so his cure he said he always used was to pour brake fluid on it while it was running and it worked right away. I am not saying it's a good way to cure it , not even sure why it does it , but i saw it and it did stop the squeeling. It was messy and couldn't be good for your paint. He does top notch work for others but like the shoe makers kids who go bare foot his truck and cars are held together with chewing gum and bailing wire. Hope everyone has a ''happy new year'' and keep those g vans going.