Weird sound from engine

Hi, I'm new on this, so I will try to explain my problem the best way possible, I was searching to see if someone have the same problem, but didn't find anyone.

The problem I have is from 2 days ago, I own an automatic Galant 1998 V6-24, I heard a sound from engine, but it appears only when revs are like 900 - 1500rpm, at 2.5k rpm and above the sound dissapears, it sounds like a whistle, something like if I had a Turbo installed on my car, but the sound is a little deeper than the turbo one, any clue of what it can be.

Thanks,