Take a look at the rear hanger. Your exhaust might be rubbing or resting on it causing the noise to transfer into the cabin. I have the same exhaust and have that problem. Been to lazy to go to muffler shop to have them remove and reweld hanger away from muffler.
Well the droning was the canister resting on the rear hanger. Transferring the vibrating noise into the cab. Which sounded like drone. Kind of sounded like when you have real stiff motor mounts.
Just a quick update on this issue. I found out why it sounded like it was droning. The downpipe pushed the exhaust a little further causing the muffler canister to be resting on the rear hanger. Now I have to figure how to address the problem.
I'll just wait till I'm 100% tuned. See if that makes a difference. I guess I'm getting older an mind loud exhaust now. I remember I had B16a straight pipe no muffler and I could careless. Lol