Hi all, ive had my golf for a few months now and being my first turbo charged car i have a question

I recently smoothed my airbox and fitted a pipercross filter, yesterday when driving the car i had the window open and heard a very clear whistleing noise between 2k and 3k revs in 3rd gear then it vanished is this normal??? I ask as it did this before but no where near as loud!!! worried somethings a miss!
Cheers
jim
