is there an exhaust that actually has a sound decrease when the revs reach over 3500 or 4000 rpm? cause I don't want to be buzzed crazy when I'm on a 4 hour drive over to vegas

or would all canister design (HKS, APEX) exhausts give the same effect? more noise at higher RPM?

 

Unless you seriously smother the sound, it will always get louder with higher RPMs... there are that many more explosions per second. But to answer your question, no exhaust system that I know of.