I have a 2006 G35x and recently when i start the car after it has been sitting for 30 min or more when im going less than 15 miles per hour the car makes a small ratteling sound and it only las like 2 seconds and than goes away. It dosn'nt come back again untill it sits for 30 min or more and im under 15 miles per hour. Anyone have any idea of what this could be?

 

It's the ABS self test. If your foot is on the brake pedal you'll feel it vibrate as well. Perfectly normal and nothing to worry about.