My initial guess, if your rear carrier is aluminum, is that it's corroding. Aluminum corrosion looks like white crusty salt. If it were diff fluid, it would leave a dark oily stain on the housing. The protective coating may be wearing off.
Well I took a closer look this morning and believe it or not, it looks like it is simply condensation from the hot parts of the car. I'm in coastal CT where it has been really humid so I'm chalking the salty taste to the humid coastal air. I also noticed a few other places on the under carriage where it's dripping the same salty clear liquid so I'm not too worried anymore. Weird.
Well, the reason it was salty is, because aluminiumhydroxide is a "salt". It will therefore taste salty.
The white dots are the mentioned AlOH³ which is normal, as aluminium will try to cover itself with a layer of white oxide to protect itself. That is why you shouldn't over do it with engine cleaning, as you destroy the protective layer. All aluminium products do this. Compared to rust, it is the healthier way
Don't worry about it. My engine is covered in these white dots already (tastes salty too)...