trucks making a chirping sound, but...
 

only when its in gear, and im accelerating (its a 5 spd). This makes me wonder if it's not the serpentine belt or a pulley, since the belt spins even when in neutral. It also doesn't make the sound when i'm sitting in neutral revving, any help?

Sorry, try more info.
Depending on the year, automatics are also five speed but I'm assuming you mean manual.
What engine?
If the "chirping" only when accelerating?
Does it increase in level or frequency with increasing speed or with increasing engine speed?
Where does the "chirping" seem to be coming from?