Buzzing? from my '92 Pickup

[Karstyl]

I have just aquirred a 92 pickup, automatic transmission, extended cab.
I am having a high pitched buzzing sound while driving, but only when going over 40 mph, it is not that loud until around 60. It sort of sounds like when one blows up a ballon and pinches the opening to let the air out. It is not louder when the window is open (tho the wind sound is quite overwelming at 60 :-) ) I sounds like it is coming from behind the dash/steeringwheel area, but I am not sure.
It seems to be affected by turning on the windshield wipers (or maybe, it did once, it was much softer when they were in the up position then when I turned them on today it seemed to make no difference, so it might have been random.) It is not affected by the truck changing gears, and I can not get it to happen when I am not moving.
I am really wondering if I need to get it fixed now, I think it might just be something that is loose, but could it be something much more important or dangerous, so I am hoping someone here would have some insight.

thanks
karstyl

[nofear4189]

air might be blowing up under the truck or something, and catching on something underneath and whistling. Id suggest looking up underneath the truck and looking for a spot where air might be able to rush into the cab (maybe directly under the dash) or near the firewall (part between the engine compartment and the front part of the dash). Also, you could pop the hood and look and see if theres a hole or something of that nature on the firewall, again.
It also may be coming from air draft off the mirrors or air rushing through the wiper arms. Next time you hear it, put your hand over the side mirrors and see if it helps. (i say this because on one of my grandpas old vans it did that, and it came from ari rushing over the outside mirrors. (whistling sound)
-Adam-

[MRDosedrvr717]

it could also be radio interference with the engine reving. Try turning off the radio or unhooking the power to it and see if the problem is still there.