Changes engine sound like vtech?

[white46]

Hello. I know this sounds funny. hahaha

I drive 03 4.6is that I fixed from deadly timing chain issue.
When I drive the car around, doesn't really matter whether engine is cold or hot, if I go over 2500-3000rpm, engine sound changes.
Like VTECH KICKED IN!

Really.
All kiddings aside, between 2500-3000 rpm, there is distinct change in engine sound, like how Vtech opens additional valve that changes engine sound. All of sudden, it changes to different tone.

First, I thought it could be the tranny issue, but there is no changes in RPM. No jumping up or down, so I don't think that's the issue.

I've been driving the car around about a year now and it's been like this some time.
Have anyone experienced such from m62tu engine?