Check your belt installation, on some models there is more than one way to route the belt. You can usually tell the correct orientation by the way the belt rides on the individual pulleys, ribbed side always rides a ribbed pulley. Smooth pulleys always see the smooth backside of the belt.
Worth a look see.
“She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself.”
— Han Solo