I have a 07 3500 with 5.9 cummins with a squeaky belt

With belt off theres no squeaking so it is the belt. But teres got to b a reaso that it squeaks in neutral but not park

In all my years of turning wrenches and that is a bunch, I have never ran up on anything like this! That dont help much i know but when you find out what it is, post those results so others may benefit also. . Have you tried it in neutral or in gear with park brake on and foot off the service brake pedal? Just thinking maybe a vacuum pump loading the belt somehow...?.... It just dont make sense! Maybe repost the question, more readers during the week. Maybe someone else knows more!

When its in gear the belt squeals weather on the brakes or not. I will keep tryn and post back when i find the problem. Thanks