my car sounds fine until i hit 3000 rpm to about 3400 rpm it make this weird noise coming from the motor and under the car. does anyone have any clue what that noise is? thanks.

 

is it a metal rattling noise? if so...its your heatshield around the cat under the chasis...remove it and no worries.

 

Its not always the head shield man, mine is the A-pipe. the inner pipe and outter pipe vibrate against each other at those RPMs. The only fix is getting a header. Probably go after market cause the OEM one is like $500

 

An exhaust rattle at 3k rpm is likely due to an internal failure of the a-pipe (2-1 pipe). There is a TSB (technical service bulletin) regarding this. Some dealers will replace at no charge. I don't think it affects performance, but it sure is annoying, eh? If you plan to get a header, just do that and don't worry about it. I doubt it would be worth paying for a replacement OEM a-pipe.
Good luck and let us know if it is indeed the a-pipe rattle.