Anyone know what it is or why I'm getting it? I'll see it after I wash the car and then just noticed it today at lunch. It's almost like rusty water coming throught the center cap and trickling down the wheel. It easily enough wipes off but comes back again. Anyone else experience this?

 

I had a bit of rusty water trapped between the hub and centercap of one rim when I took my wheels off the first time. No dribbles while mounted, though.

Once I take a rim off, I smear some anti-sieze on the surfaces that the wheel and hub interface at. Aluminum, steel, and water act like a battery, and usually the aluminum loses. The anti-seize minimizes rusted hub surfaces and stuck-on rims.