I just recently added the Magnaflow cat back system to my 545i. I am pretty please with the sound. It isn't extremely loud and it's not rice sounding. Very clean tone.

 

Same with my magnaflows in my quad setup, but there is a slight drone at speed.

 

RPI drones from 1500-2000 rpm roughly. When I cruise at 70 here my car is above 2k. Are you going faster at a lower rpm?

 

Good question, I have the exact same car as the OP, and mine cruises at 85-90 @ ~2500 RPM

 

no im in 2500 hundred when im doing 80 highway might not be an issue city driving might be

 

bro
get a rpi, put it on to see how u feel about the drone, the drone only happen when the rev drops down to certain level, i forgot mine was how many rpm. once u press onto the paddle abit, the drone gone.
if u sure u can't stand for it, then get a x pipe. but the x pipe will kill about 1/4 of the original sound.

more over, i kill mine original resonator and replace to a high flow muffler. sounds more good, hehe