When in drive, something is out of balance in the rear of my 1989 Chevy van. It sounds like a worn belt on the tire, but I have new tires. It’s an intermittent sound, mostly at lower speeds or when slowing down. At high speeds, it starts to turn into a whirring sound and then disappears and then the car rides smoothly. I don’t think it’s coming from the wheels. I’m suspecting the drivetrain. It’s a two driveshaft setup w/ 3 Ujoints. It also has a bearing that the 1st, shorter driveshaft rides in. Would replacing the Ujoints make any difference?