my dad has an ST220 and at the top of the rev range it makes a loud noise(asif your blowing across the top of a bottle) and it keeps making this noise all the way back down to idle. its got a pipercross velocity intake system on it and milltek exhausts.
it still makes the noise with the V.I.S disconnected and just the maf showing.
does anybody have any ideas to what it could be?

thanks.
Rob