My 2004 Mustang has a very annoying drone from 2000 to about 2004 RPM's. On the Allfords forum, I have found many complaints of the same drone, and the answer is adding a resonator pipe of about 23" to 28" that is welded into the exhaust pipe near the rear of the car. This is a pipe same as the exhaust, and functions like the plumbing pipe extension on newer homes where the washer connects to the water supply. For the washer, it prevents the noisy slam of water pressure hitting the washer inlet.
I have talked to 5-6 muffler shops and auto shops around town, and no one wants to touch it. Does anyone know of a shop in town who is familiar with this problem and is comfortable doing the work? I have drawings and specs for the shop to use.