Flowmaster drone solved.

I am the OP and I should have updated this thread. I run 340 hi-po manifolds 2 1/2" exh and H pipe with tips on my B body. I wound up removing the flowmaster 40's and going to dynomax turbos for sound and better flow. Drone solved. Only issue now is that it was too quiet for my taste. Well last week I installed Flowtech ceramic coated headers that I bought at a swap meet years ago. Wow. Huge difference. Sounds proper now and added seat of the pants torque. No drone. Its a nice mellow rumble but barks when you get into it. It would sound even better with a nice cam. I highly recommended but if you prefer the something louder the Ultraflows. I always heard that the 340 manifolds flowed as good as headers but I don't believe that to be true.