I have noticed since last six month there is unusual sound coming from the car and you can only hear clearly when taking gas pedal off. I took to the exhaust repair shop, one suggested resonator and other didn't see any issue with exhaust.
The found is like humming sound similar to sports exhaust. I suspected it could be transmission and changed fluid but the sound is still there. What else to check.

 

Speaking from personal experience my advice to you would be to check the fly wheel and the pressure plate mine is doing the same thing currently

 

Thanks Dani.

 

Loose exhaust heat shields rust eventually leading to rattles and such.

 

Fixed. The transmission mount bracket bolts were loose and making noise when accelerating. After replacing failed mount all the noise gone.