Well the other day i went to get alinement and when the guy was driving the car on the ramp the bottom of my car hit something and now my car sounds like one of those beat up hondas..(only up too 3k rpms) and i need outer tierod ends..

I jacked the car up and looked under it while the car was on but i cant figure out where its coming from..will a cat back exhaust fix this? or you think its further up front? Also i dont want to sound like a ricer so should just get another stock exhaust?

 

You have a hole in your exhaust. Inspect the undercarriage (most namely the exhaust components). Find where it's damaged, and replace it, or if it's small enough, have an exhaust shop weld (fix) the leak.

 

if he bottomed out on the rack they should be responsible. it probably hit your resonator if you have stock exhaust, thats the lowest part usually. check the rear section from the cat back with it running. dont get ebay exhaust, just replace whatever it is with stock ish...........

 

oo ok is obx a good catback?

 

also one more thing when im playing music loud theres a knocking noise coming from under my car..like i also hear it when i close my doors..I believe i shook something loose under my car..(exhaust maybe?) its like my baby is falling apart

 

As NmexMax said, inspect the underbody. That's the only way of telling what's been damaged.

Also, for you exhaust questions:
http://forums.maxima.org/showthread.php?t=322569
http://forums.maxima.org/showthread.php?t=385887