I was talking to an custom exhaust builder and found out the TRD/Borla dual exhaust cat back has 2 cats built in after the muffler. He believes that is the reason there is so much drone at the 1800 rpm mark. He also said this cuts down on the sound significantly. THey are not sensored and really arent needed. I changed out my muffler with a magnaflow and they are removing the 2 cats on tuesday. I may be late in finding this out just thought I would share this with you. I will let you know if it makes a difference not having them.