We're talking about the single rear-can part of the AA Signature kit. With valves closed the pulses do a 180 bounce off the side of the can. It causes a reverberation. OP got the catless DPs so the pulses are stronger and annoy him. Drone is more the under-car buzz or hum that can come from non-res midpipes (like catless DPs with the AA single mid).
Usually people pair the Signature with stock cats because the Sig seems to amplify volume while lowering tone. I used 200cpi sport cats and it does get attention, but I did it to improve turbo flow while keeping stink down. On several drive/cruise meet ups guys behind me said "that sounds damn good and mean!".
