everytime it rains out side, my engine seems to have a slight whistle or squeak coming from it. i'm assuming water is getting in somewhere, but it may just be nothing. any thoughts in this would be helpful, as i do not know if this could be serious or not

 

Check the bearings on Alternator, Idler,Tensioner etc. Some times when they get old and dry, they start making noice with humidity. I have that problem during winter.my tensioner bearing and Idler squeak for few minutes every morning. after they warm up and dry , go quiet. Then i know its time to replace them.

 

How old/ condition of belt?

 

not sure how old, had the truck since november, and it has 30,000 original miles, so its possible it could be the original one. i'll check the condition of it this evening.

 

That's probably your cheapest & easiest date! Also a common factor.