ZZP has the best coupler on the market now. this summer, i thought my coupler was going bad, after taking the belts off, i found that the balancer was broken, the rubber breaks, but about idle, the noise was gone. this is a common problem that GM redesigned the way they use the rubber section now.
what mods do you have so far, a smaller pulley alone wont give you much, with it , you need to improve your airflow in and out of your motor, and trust me on this ok, cold air is your friend with a smaller pulley, insulate everything on your intake system before it gets to your SC.
KR is a power killer and heat is the main factor of that.