Weird Sound Behind Drivers Seat on floor-Resonator?

[LNGfish]

Hello,

This sound can only be heard inside the car with the door shut, you can not hear the sound from outside of the car. To best decscibe the noise I can call it a popping low tone noise. Sort of what you might hear with a hole in an exhaust pipe. I listened to the sound of the Trannie Flex Steel plates and it is not that sort of sound at all, my sound is much lower in frequency in tone.

I have had it on a lift at (2) muffler shops and there are no leaks to be found.

It makes the sound in neutral as well as in drive and the sound goes away above 1,550 rpm. It is louder when in Drive and accelerating. It is not a new sound at all but trying to isolate it finally.

Is it possible for the Resonator to be bad and if it is bad to only hear it on the inside of the car? ie the sound is projected up to the Floor Pan behind the drivers seat?

The fellow at the muffler shop is perplexed as much as I am.

Any assistance would be much appreciated!

Thanks!