GMC Repair: Noise when accelerating, high pitch sound, gmc 3500

Question
I have a 1998 GMC 3500 series box van.  The van has a 350 and an automatic transmission.  My question has to do with a noise that the van makes when it first accelerates.  A high pitch sound occurs when I take off that to me sounds like a vibration.  The noise only lasts at speeds below 10-15 mph when accelerating.  The truck shifts fine and makes no noises once I am going.  Also the noise seems to be coming from underneath the truck.  It does not make the noise if I simply rev the engine in park.  Thanks

Answer
Hi
I wish I could hear the noise.
Does the truck actually vibrate? Can you feel a vibration like in your feet, the steering wheel or the seat bottom?
If it is just a noise, I know these vehicles do make some noise when accelerating, usually a drive shaft resonance.
Please follow post back, if needed.
Good Luck
Pawl