shut down

so we're driving along coming home from road trip listening to music and using the nav, when all of a sudden no more music, look over screens black... after a second, its the blue sky background with mazda logo, then the audio screen is up saying 'audio off' in the middle push the power button...

2008.5 Mazdaspeed 3 / 30,000 miles / Recently, I've been getting a slight rattle from my engine on shut down. Is it a motor mount? Something loose maybe? It happens randomly, more often when it is hot i think. Any Ideas?