i recently hacked off my cats and now when i get to around 4000 rpm's and higher i hear a rattling sound. Is this valve rattle i hear or what? I never heard it before i cut the cats off, did they always rattle like this and i just didn't hear it because of cats still being in place or did you think i screwed something up by doing this?

 

Did you weld a pipe where the cats used to be or did u use exhaust clamps?

 

i welded a pipe

 

You might be hearing spark knock (pinging). Your PCM may have to adjust to the improved exhaust flow or you might have damaged a sensor somewhere. Isn't the O2 sensor next to the cats? What type of gas are you currently running?

 

I'm only running 87 because the truck is stock other than exhaust

 

did u disconnect the o2 sensors from the harness or are they still strapped up there somewhere... i have an annoying sound coming from the ring around my o2 sensor... makes vibrating noises at idle and you can hear it on ever little bump in the road (but mine are attached).