whoosing

Hi all New kid on the block so bear with me. Noticed last night that when I power on above 2500rpm I can hear a loud whooshing or sucking noise coming from what sounds like behind the glove box. It doesn't make the noise when static and revved only when driving. Could this be a leaky...

Posted here because not sure where else to put it. S211 320CDi I6. 166000mls. Valeo has been done. No accompanying vibration. Undertrays are in good cond and fully bolted up. Noise is similar to the 'hunting' or rhythmic drum sound you get when a rear side window is open slightly and is...