Magnaflow muffler ....

IIRC the drone is caused by the pipe dynamics. Ie. if you have no pipe out the muff, it sounds terrible. There was some formula out there that took exhaust duration and header/pipe diameters into effect and told you where you could terminate the exhaust (add expansion/muffler) 'between events' for no resonance. sort of like painting your collectors and flanging them where the paint burn line ended up.