Chevy & GMC Vans

Hello all. On very humid days, or when my Astro is left on a grass field overnight or when it rains, it makes a squeeking noise when it is running and eventually goes away within 1/2 hour after engine warms up. I am guessing it has something to do with moisture in and around the engine. No sound when it is dry and sunny. Would like to know if anyone else has experienced this and what problem this would indicate. I am inclined to suspect something to do with belts? Any help would be appreciated. Thanks.

sounds like belts, idler pulley, or alt bearing to me. I had chased the same sound in my van for 5 years. New belt every spring would make it better but the noise would always return. In my case it was the alternator bearing ( found it with an automotive stethoscope ) so I left it until the unit failed.

Take off the belt and spin each of the components to feel for any roughness in the bearing