A too tight belt will make a loud whining sound. I had brought my 2010 Nomad in to my dealer for a belt check up, and they adjusted it, and afterwards the whining sound aroud 45 mph was terrible. It took those idiots three tries to get it right. I knew it was too tight, and I should have done it myself.
I recently had the Commander II's installed by a local mechanic and he got the belt right the first time. So, it is not your tires.
I will never go back to my dealer for anything, ever.
Take care, Eric