easyscoob

i have a 2005 wrx ppp lately the bailey dv has been acting up like when cruising at 70+ mph it just lets out a long hiss for about 2 or 3 secs sometime on coming out of junctions or trying to pull away with the foot down it will pause, hiss/whoosh then the car will lunge forward as normal. do you think the valve is getting stuck and just needs a good clean or is the car producing too much boost i dont really know please help