The rubber is optional...I'm not using it and don't hear any noises. Of course my car is insulated pretty well and my exhaust isn't real quiet either. I'd pull down one strap at a time supporting the tank and cut the rubber. It's going to be tough otherwise.
I thought about not using the rubber, but I didn't have it on the original and the noise drove me nuts! I will see how it looks after I trim it, and go from there. I am thinking I can slide a thin piece of steel or aluminum plate under the rubber, then run a razor along the tank strap to trim it.