Muffler noise

Last week I had a magnaflo muffler put on, wanting to open things up and let the Supercharger breath a little better. My goal was to improve performance but not at the expense of two much noise. Noise being subject to each individual taste but after install I had one complaint. Between 1000 and 1500 rpm not the best harmonics when easing off the line normal like.

A little investigating and I dont think it is coming from the tail pipe but rather the muffler itself which gets amplified in the cab. experimenting with materials I have laying around - what I have done is place angle iron on the top side of the muffler , strung my hose clamps together and snug up the iron with a cut up strip of exhaust gasket material I had between the hose clamp and the muffler on the underside.
What I was attempting to do was to see if the muffler case was passing harmonics through and this "fix" seems to fix what was bothering me. I am going to need to pick up some more hose clamps and run a second band on it but I thought I pass on the tip.