Mufflers Without a Drone

What can I do about it?
Not much. You can't really block this frequency range because it is a natural resonance frequency. It will rattle EVERYTHING (even materials like wood and some softer materials as well). Dynomat in your trunk won't work. Dynomat on your floorboards or on the unibody underneath your seats won't work. This range of 133 - 138hz is incredibly difficult to manage. The best way to address drone is with muffler design or resonators. The factory mufflers are specifically designed to not only block but also CANCEL these frequencies. Some aftermarket designs such as Borla's and Corsa's offerings do the same job. Borla's design cancels out some of these frequencies as well as ensures that the sound energy is going out the tailpipes. Corsa's designs have an internal chamber that is of the correct length to cancel this frequency out using the laws of wave reflection.

Designs like the Magnaflow Competition Catback that uses a 5"x14" resonator to attenuate the engine sound drone like a mad cow. Flowmaster American Thunder mufflers drone like crazy because they were designed to produce a specific sound that was focused on the outside of the car. There's nothing wrong with this, it's just what the manufacturers decided to produce. If you have an exhaust system with one of these such designs and don't want to change your entire system, then a set of straigh through race mufflers such as Dynomax Race Bullets or Pypes M80 mufflers will give you some relief but may not completely eliminate the drone depending on your overall setup.