Drone is, basically, the sound bouncing around in the pipes. Performance mufflers don't do much to help curb this. Most big cars and A LOT of today's full size trucks have resonators somewhere in the system, generally in the longest section of pipe. I sell exhaust for a living, so this kind of question comes up almost daily. Flowmaster's chambered mufflers{unless you opt for the 50, 70, or 80 series} will drive your wife crazy. Magnaflow is a different type of muffler it's got a perforated tube surrounded by fiberglass. This design is quite a bit tamer, so to speak, size for size with Flowmaster. The larger the case, the quieter it will be. Most mufflers get larger in each direction the longer it gets. So, say you want a 22" long case, well then the oval will most likely be a 5x9 or larger oval. Which probably won't fit under your car. I can't speak to how your current mufflers are configured, like a center inlet\offset outlet or the oval and length dimensions. Get these measurements and visit Flowmaster's website. They have a "find it by dimension" page. Start there, then see what others offer too. I will end with this, my 75 Royal has a 400 and a single exhaust. The previous owner had the exhaust replaced from the Y pipe back, with a 14" Turbo muffler. At speed you can only hear a hum. At idle, it sounds great. I'm sorry for the lengthy reply, but it sounds like your choice is really important in a very personal way. But, please keep in mind once a muffler is installed and used it's yours. Choose carefully. Good luck.
