Is there a reason why I wouldn't notice the problem when revving out of gear though? I can only notice it when car is under accleration.
Definitly. That's what mine did. My take is that it is only under acceleration that additional air is trying to enter and thus escape the engine. The whooshing sound is the air trying to find another escape path. Once you let of the accelerator pedel (which is of course really more of an "air" pedal than a "gas" pedal) you reduce the air that is trying to be forced out of the system and thus reduce the pressure and the noise subsides.
