when i am driving from 3 to 4k rpms it makes like a loud rattling sound and it wasnt to bad when we first bought it a month ago and now its getting worse and i cant figure out what is wrong with it and just last night it starting doing it 4500 to 5k rpms also now if anyone has any idea what it could be please let me know thanks

 

Hard to tell without a recording... is the rattle mechanical as if the valve train were loose?

Have you tried to locate the source of the sound? i.e. open the hood and see if you can tell where in the engine it's coming from? Or, do you only hear it when the car is rolling? If so maybe something in the transmission or drive train.

More data.. ; ' )

 

it is coming from behind or below the engine somewhere and it is more of something is loose but it only happens between those rpms and you hear it anytime you rev the engine whether its stopped or rolling i really think maybe something is loose on the exhaust or something but everything is tight so i dont know

 

Sounds like a heat shield....

 

Heat shield on your catalytic converter

 

It's probably the infamous GS-R header rattle, where the inner wall of the exhaust manifold comes loose and rattles inside the outer pipe at certain RPM's. That is, unless that was revised and fixed before the 98 model year.

I've had 2 OEM manifolds, both repaired, and both developed the same rattle again.