Just redo my Exhaust setup to battle drone. And after a few trips to the muffler shop and countless search for Drone issue. Here is my final result:

1. Read the below link to understand the drone calculation:
For All You Mustang Guys With Exhaust Drone - TrueStreetCars.com

2. Take a look at my Frankenstein's Exhaust after a few trials and errors to get riddance of DRONE. Some installed the Resonators by the tailpipes, I have space issue so I installed it right after the muffler. It's very tamed now, but still is very PPPPuring. Kind missed before the resonators installation, but have to do it for the Kids. I'll upload some sound cliff when I get a chance. THE DRONE NOW IS LIKE ALMOST NONE EXISTENCE, that was what I'm aiming for. However, mine is 530Xi, since yours is 545i, this setup should sound better than mine.

 

Holy Crap! Ya, I'm not doing that. Mine is a cat back exhaust with one muffler. If Magnaflow cant help me with it, it will be coming off. I wanted a little sound this system is ridiculous.

 

Haha my bad, I thought you are doing the whole new cat-back. If only the muffler, the sound will be NICE. But it will drone. I'll redo mine to make it more nice and neat, or maybe not. No one going to see but me and my mechanics.