I went to a muffler shop and got a custom cat-back exhaust, 2.25" piping, new hi-flo cat (magnaflow), and a flowmaster muffler w/ magnaflow tip.

when i first got the exhaust it had the same consistent tone at all rpms, but now about a month later the exhaust seems quieter, almost stock sounding, but at 4500 rpms vtec screams like a type-r on steroids, it sounds good but whats with the huge sound change all of a sudden, also i had a new zex cam put in, (this was before i got this exhaust)

 

What probably is happening is that all the inside of the muffler has burnt out it happens to all exhaust. Either it sounds loud or quiet its natural. It usually takes about a month or a cupple of weeks to get the inside of the muffler burnt out. Enjoy the sound.