Rattle at Startup on 2001 Altima

My 2001 4cyl. Altima emits a noise from the passenger side when started. It seems to be in the rear of the left side. It lasts for about 3 seconds or so then stops. When immediatedly restarted, no noise is heard. If it sits for about 30-45 minutes the noise at startup returns. I have also heard in on occation during acceleration when under a slight load. Other then that the engine runs fine. My trouble light is not on.

Any suggestions on what may be causing this noise. I've got 75k on the car and bought it new.

Thanks in advance for your help.

Fourzs

Much like all Nissans its probably a loose heat shield on your exhaust or catalytic converter. Hope this helps.:)