Not sure where to start with this...

I have the Spin Tech muffler. It's one of the best flowing mufflers you can get, and has a decent sound. Not a deep rumble like I was hoping for, but I can live with it. When I got it installed I had them leave the cats off. Only it was way too rattly and annoying sounding for my taste. So I had them weld them back in. But, when they put them in, I' pretty sure I noticed a loss in power.

So I'm trying to think of a solution. Is the solution to eliminate the cats and maybe use a different muffler - or is it going to be rattly regardless if I don't have cats? I know you can hollow out the cats and Allen can delete them so it will pass inspection. But if I do that, again, will they still be rattly?

Any solutions I'm not thinking of?