What could be the cause of a tweeting sound from a 98 Sentra whenever it rains or there is dampness in the air?

well check your belts if they are loose then that could make this hapen. if the belts are not loose look at the pullys if the pullys are shiny like they have ben polished then you need new belts they are old and worout. if this dose not help then check the berings on the pullys if there is metal shavings eney where then the berings are gone but i dout that is what it is doing this the belts is my best guse