its the tiny muffler thats the issue, get a semi straight thru one,
my system has a hotdog resonator and a big oval muffler, the muffler is what muffles the drone the most, get a muffler thats semi striaight thru, so it curves inside, that will forces the gases to be muffled but not restricted , then your drone will come down ..
you need a either a large oval muffler or resonator .. police come straight after noisey cars..