I fought your same problem with my 70 Challenger with the TTI 2.5 and manifolds, both with just the Dynomax and with resonators behind the dynomax.

my car has undercoating and I had lined the interior with sound deadening/heat blocker and from 2K to 2.5K I had a drone so bad my ears would ache all day after just a 20 min ride.


I finally changed everything to a stock style exhaust from Accurrate LTD and now it is a pleasure to drive.