01 WRX vacum cleaner!!

[Furyblade_Lee]

Hi guys! I have an intermittent problem with our bug eye WRX. It is totally un modified, and will drive normally with full power for days on end. But sometimes it loses power to the extent it will not accelerate, and makes a noise that is best described as a vacum cleaner! The noise rises with the throttle pedal position, not rpm or speed, to the extent you can play a tune on it. Then lifting and changing down sometimes cures it. Other times you just have a faint noise and small loss of power. First I thought it was a split hose or something but that would not go away? Could it be the dump valve sticking open or something? No expert on turbos!