Originally Posted by TheOtherDave™
The sound you're hearing at 4500rpm± is that of the secondary intake runner valves opening.. just before the VTEC switchover.
The CAI has eliminated the baffles and resonators that otherwise mask that change in the intake note.
The cam changeover occurs at around 4500 and the butterflies open up around 5700 rpms, so what he is experiencing is normal vtec engagement.