Not every Flowmaster has a drone. They are mass produced big time. If the separating walls of the chambers are not installed at the right angle, they will drone. Also, mufflers are like drive shafts. All drive shafts vibrate somewhere in RPM. We simply tune them not to vibrate within the RPM where we use them. Same is true of mufflers. They can all drone under the right (or wrong) circumstances. It's a frequency thing, much the same as a drive shaft vibration, but created by exhaust pulses instead. Pipe size, tail pipes (or lack thereof) crossovers, and many other variables can help or hurt where in the RPM range a muffler drones......or does not drone. I am sorta in the "I don't care if it drones" crowd. I sorta like it a little bit. Also one more thing that no one has addressed. WHERE the mufflers are installed. Wherever they are, you will have a rumble. Put them under the driver's seat, for example. lol Compared to being just in front of the rear axle, they will be LOUD. This is why header mufflers usually drone and you cannot get rid of it. You are simply right on top of them.