Need more info to help you locate the trouble.
IE

Automatic or Standard?
Do you hear the noise at idle?
Does the noise go away when you take your foot of the gas and just coast?.
Does the brake pedal feel like it pulsates when you push it?
Does the noise go-away when you brake hard? Gentle?
Do you hear it when the truck is moving or all the time, sitting still and gets worse as you drive? <img src="/forums/images/graemlins/confused.gif" alt="" />

The noise is something that I have never heard myself, but
I owned an 85-720 and a 95 Hardbody. With the noises these 2 trucks made I might be able to help you locate the trouble.