I have auto and the single Borla exhaust and very minimal drone (stock 2nd cats INTACT still).
However, when I had the 2nd cats removed, it droned like a bitch and gave me headaches everytime I drove my car. I now have the stock 2nd cats placed back on and love the Borla exhaust now.
Like what Mr5 is saying, you will drone no matter with auto.
2014 F32 435i EBII / Coral Red