I'm experiencing "grunting" when tonguing in the clarinet's high register. How can I fix it?

Hi, I'm a sophomore clarinet music major and I'm having tonguing problems. It's been something I've been trying to diagnose and fix for awhile but it hasn't gotten better. I'm trying out for wind symphony tomorrow and I know there's no quick easy fix for this, but when I tongue the high register notes they are accompanied by an annoying grunting sound. I'm tonguing as lightly as possible, touching the tip of the reed while still keeping adequate air flow. My embouchure is good and I've been playing double lip. I make sure to keep my corners firm and to not move my jaw. Also, my setup is a Pyne Bel Canto mouthpiece with a 3.5 Vandoren and a Luyben ligature. Any input is appreciated! This is a very frustrating problem!