Suggestions for muscle car sound muffler without drone

Incase anyone would like to see the plot after the side branch resonators see below. It's difficult to keep all the conditions the same for the data. It may not have been taken on the same road area but it was done with the windows down and going up an incline like the rest of the plots. Different road noise levels can bias the plot up or down compared to the others but you can see how the peak of the drone has been cut down. As I noted to your ears it's gone.