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It's hard to know what itIt's hard to know what it might be without a photo. The rainiy/humid conditions would seem to encourage a fungal disease. Some fungal growths aren't as fuzzy as, say, what you might find on old food. Downy mildew is common on beans--could it be that? Powdery mildew does better in cool weather, but it might be a possibility. Rust can sometimes start out whitish. For more information about bean diseases in your area, you might be interested in this from the Alabama Cooperative Extension:   http://www.aces.edu/pubs/docs/A/ANR-1024/ANR-1024.pdf   It doesn't quite sound like insect egg clusters, or residue from pesticides, salts, etc. For further advice, you might ask a local nursery or call your county's Cooperative Extension:   http://www.almanac.com/content/cooperative-extension-services