No it is not a belt issue but i noticed the excessive belt whipping, When you run the Ultimx UXP446, XTX2236, 30C3750 then it is wise to shim the driven to remove some of that excessive slack from the belt. That shift rod has a couple adjustments so set it in N and then move the lever all the way and make sure rod ends floats and then all the other way and then check again.