Just got off the phone with Borla! L99 + AFM look here

[HeavyD]

Hey everyone. I emailed Borla the other day regarding their systems and numerous complaints from other members about drone and how AFM sounds. They asked me to call them back for a chat. I talked to Chris and he was able to shed some light on these issues. First, Borla will not be making a kit specifically for the L99. He basically said there usually isn't drone, but there may be some weird resonance caused by AFM at certain rpms, he said usually around 2000. From their experience they claim almost all manufactures will has some type of resonance from AFM, even Corsa. As for how badly AFM sounds is almost dependent on how the owner perceives it. He basically said, that you have opened up the exhaust, you have made it louder, it will be louder! Some members here don't mind it and others had to go so far as to take all their aftermarket stuff back off again. He did have some recommendations. If you plan to use LT headers you might want to try the Touring system instead of the sport. With headers and elimination of the factory cats you have really opened up the exhaust flow and the sound flow too. It may be simply too loud and agressive with the sport system. Anyone going with shorties should be ok with the sport system. They are not big fans of AFM either and say if you don't like the sound AFM makes then to tune it out. As for any drone or bad AFM noise that is there they do make a venturi piece that slips inside the pipes before the mufflers and gets tack welded in. Part Number is 41850. This will most certainly eliminate any problems.
I still look forward in members making videos with their L99 and any drone or AFM noises.
I hope this information helps!

[mlee]

Pretty much sums it up... I was told the same thing about LT Headers. My decision is to tune out AFM at the same time I put headers on... For now I'm quite happy with Corsa