Where exactly is this hole located on the t/b? Are you talking about INSIDE the t/b, like the hole marked lower port in this pic:

If so, that's supposed to be there, and if your intake is modified, then the sound of manifold pressure going from vacuum back up to atmospheric when you turn off your car will sound like a whistle as the air moves thru your filter element.

If the hole is on the exterior of the t/b, then its exact location would help in determining its purpose.

There shouldn't be any holes on the exterior of the t/b that would "suck in air", unless your MAP sensor isn't in place, and then you would know with the CEL blaring in your face.

See if you can pinpoint the location of your "hole" in this pic: