When my LS hits 4000 rpms there is this rattling coming from it sounds like under the shifter somewhere but it is only there at 4000rpms, Can somebody help b4 i burn this thing it's driving me nuts Could it be that cat or no?

 

Heat shield maybe?

 

Try removing your catalytic converter heatshields...both top and bottom. If that doesn't work, remove your exhaust manifold heatshields. Then go on to the ones that line the entire exhaust piping...notably the one next to the shifter linkage. Do you have an aftermarket shifter or exhaust?


[Modified by Dozed, 6:26 PM 3/28/2002]

 

Your resonator could be bad as well. I have had to replace that piece before on one of my cars. It took forever to find out it was cracked.