i just got a bbk cold air intake for my v6 mustang it drives fine but when i start it up it makes a rattling... what could this be?

 

Welcome to MF!

Did you make sure to re-use the rubber isolators from your stock intake?

If you did then take it back out and put her back in, be sure its not touching the strut tower or any other part of the chassis.

 

yep just tighten everthing back up. could be a loose heat shield.

 

Check to make sure its not rubbing the ac line, or some line that runs real close to the intake just infront of the MAF, i know mine is close ~ 1in.