Car speakers crackling?

I think the installer was in a hurry and didn't cover all the wires. The stereo could have pinched a wire if it was a power wire or a speaker wire that could be the smell you are getting, the rain could just be a fluke, The way you described it I am pretty sure you have a bare wire touching some metal, Like the other guys said, take it back to your installer, good luck i hope this helps.