I was not a big fan of the exhaust drone that was there at the highway cruising speeds. I like the noises that the car makes under acceleration (I never listen to radio and drive with windows down when possible lol), but I was looking for ways to reduce the drone.
For those who are in the same boat with me, here is a cheap, easy, and rather effective solution:
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I bought this 4.5'x4' sheet of MLV ^^^, cut it a bit to fit, and put it in the trunk underneath the rubber mat/tray that I had already. A foot-long or so flap went up against the seats. No installation to speak of; you can't see it; if I want to remove it, I can do it in 40 seconds or less. The exhaust drone is significantly reduced. The "good" exhaust sound is, of course, also muffled somewhat, but it's still there (especially with windows down).
Hope it will be useful to those who would like to do what I did.
Note to those in the "the louder the better" crowd who are itching to say something along the lines of "go get a Prius/Lexus/whatever": this thread is not to discuss the merits of louder or quieter exhaust (to each his own), but to help people who may find it useful.