My fellow West Chester Jetter...the Borla and race header is LOUD
I don't recall it buzzing too badly though. Brand of race header will make no difference in sound as they are pretty much the same. If you need a hand putting it on let me know...I have done header installs before.
i've got the stock flex pipe still...so i think that is what's causing the "buzzing". My theory is this....the air is moving from a large diameter (the random tech cat) to a smaller diameter in the stock flex pipe and this is causing the air to become turbulant and speed up....basically too much air is being pushed throuhg it.