Ok here what happens when I shift and go into high rpms I hear a rattling noise comming from the engine. But if I shift normaly at low rpms then I dont hear it really at all. Now could it be the tranny or could it be a heat shield rattling. I took one heat shield off that connects the cat to the header ( I have a 96 dx ) Is there another heat shield near the engine underneath there that could be the the problem. Im just wondering cause today when I was at a light I could hear the rattling when I was stopped in gear. Any help guys? Thanks

 

doubt it's the trans... might be the cat itself. go under your car with a rubber mallet and smack the cat a few times... if it makes noise... you need a new cat. otherwise look for other loose items like heat sheilds or brackets... maybe a bolt came loose on the exhaust... pretty much trial and error will fix it

 

thanks