I have a basically stock 400 in an A-body and full to the rear bumper 3" TTI headers and exhaust with an "H". This car does not drone at all now. When it was installed initially I hadn't used the headers yet but the same 3" exhaust behind manifolds and an RV type cam was terrible drone. I asked TTI about it and wondered if I got the quietest muffler they had? They said that I was sold the quietest muffler they had. It is either Magnaflow or Dynomax. I told them what I planned to do when I got around to pulling the motor and they said wait until you put that big cam in it and those headers and all that will go away. It has. I think this has more to do with a performance type exhaust behind a low performance camshaft.