I'd have to hear it.
Have you done any mods, like a gutted air box? If you're getting a strong whistle, but aren't having any operating problems, it'* likely in a secondary system. If it was in the upper or lower manifold, both the MAF and MAP would be getting fooled and you'd have operating problems. It were a leak in a seating on the throttle body only the MAF would get fooled and the PCM could still come close with fuel trims. Generally speaking the main problem with vacuum leaks is that you usually CAN'T hear them.
A historic and prevalent "whistler" has always been the PCV valve. I'd pop that out and make sure the two rubber O-rings are intact. Shake it to make sure it rattles so you know it'* a free valve. If there is any question, replace it for some light bucks.
Just make sure those o-rings are OK and in their proper places.
1995 SE ..Green and Rattle Can...234K mi...Bonnie (she'll outlive me)
1998 SSEI .. White ..119K mi...Evey
1996 SSE ..MajTeal..157K mi...4/12- Dealer trade full of Lucas Trans fix