Strange whistling on passenger side

[demccus]

Ok...this just happened on Friday and I don't recall doing anything out of the ordinary...so, needless to say, it's a head-scratcher. Anyway, when I take off hard or jump on it and get the engine to rev over 3500, I start to get a whistling noise on the passenger side (sound like it's coming from under the dash near the heater core area) that gets stronger as the revs go up and will disappear during the shift; comes back once the revs hit 3500 again. It makes the same sound as wind coming through a partially opened vent window.

It's a 460 FI automatic. 1997. I'm stumped... Any thoughts?

 

[1985 Ford F-150]

Sounds like a vacuum leak under the dash to me.

 

[radialarm]

Slap the passenger and tell them to stop whistleing!!!