corrosion

Buying a buddies 2011 JKU and sorting through the "Small things" together. We were talking bout this white corrosion coming from behind the mirror mount and dripping onto the hinges...specifcially on the driver side. Reminds me of mineral sediment buildup and if so can it be cleaned with such...

So, I've never done any rust cleanup or preventive before. Just bought a 2007 wrangler and it has a little surface rust on the undercarriage. I'm currently cleaning with a wire brush and was just wondering, when it came time to paint, how did you all keep the exhaust clean if using aerosol...