Advice

Rattling at startup could be caused by a loose timing chain. Could cause hard startihg too but may not be the cause. You need to fix this if it's the timing chain. The white smoke is probably not the timing chain but rather oil, transmisson fluid, brake fluid or coolant getting into the combustion chambers. If that's the problem, you could have an expensive repair in store. If it's brake fluid, it's probbly a bad master cylinder/brake booster unit. If it's internal in the engine, it may be time to think of a guaranteed used engine or replace the car before the motor gives up the ghost. Here's a directory link for you: http://repairpal.com/nissan-repair-in-dallas-texas