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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.

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If I can't get it to go away that would be my next option...

Lots of good suggestions on here but I have pretty much done it all except change to a different style of muffler. I have undercoating on the underside of the whole car AND the topside of the floor with insulation under the carpet, I went from cheap turbos with a single layer case to Dynomax with 2 layers, I eliminated the crossover, I added resonators, all with no change except a slight reduction with eliminating the crossover. Tis hard for me to add anything under the headliner as I don't have one....

I was unable to find any quiet mufflers that would fit, however I did talk to someone at a speed shop about different mufflers, he suggested I try Magnaflow instead of Flowmaster.

I picked up a pair of those and will let you know how that goes.

If anything is going to work I think it will be them as the case is packed with insulation which should deaden any harmonics..... I hope.....

Or I might have to put an amp on my AM 8 Track!