funny sound at 3800RPM (sounds like vtec)

[MWAKU]

i just filled up petty, and just gave it a hit, and realised that around 3800RPM, the car made this wierd sound for about 200RPM, until 4000RPM. it kinda sounded like metal vibrating when i first heard it, and like it was coming from driver sound, around the intake

i have the stock intake pipe arm, only a K&N panel filter, so i dunno how the sound can be coming from my intake

after trying to hear it a few more times, and hitting vtec after, the sound is similar.

so it sounds like, vtec for 2 seconds, but more, tinny?, when i rev to 3800, then when i get to 4000 the sound goes away, then around 5500 vtec kicks in, like it usually does

ive had the car for a year now, and this has only just happened 2nite, i'll check if its still happening 2morrow but yeah

anyone have a clue what it mite be? ( i popped the bonnet and everything looked fine .. though it was dark, but everything is bolted on sturdy, as i thought it mite be something loose)

btw the car is a bb6 vtir auto, and it only noticeable in gear 1 and 2, gear 3 is less, gear 4, no sound other then the usual

and driving normally is fine, nothing out of the ordinary