Cure for Drone
I have installed the Mad-Dad mid-pipe also. Greatly reduced the drone but it is definitely not gone completely. It exists in a norrower RPM range but is a touch louder than stock under very light throttle. With slightly more throuttle it almost disappears.
Dinan has released their new exhaust for the 1M. It has a specific chamber designed to eliminate the drone. I went by there today and they said it has effectively eliminated the drone completely. They had their 1M appart for additional parts development so I was not able to take it out for a listen. I plan to go back in a couple weeks for a first hand listen. The exhaust is BEAUTIFUL!! (as are all of their other 1M bits).
Drone or not, after 3-M3's (e30, e36 & e46) I am totally intoxicated by the 1M. My favorite BMW to date.