Recently I started to hear rattling in my transmission when I am parked in neautral. While I put it in the 1st I hear same rattling noise.It doesn't sound like grinding but when I have it in neautral and move the shifter right to left I hear it even more. I've installed a short shifter about 6 months ago and also I always had problems shifting when its cold.

 

Did you bend/cut/remove the cat heatshield when you installed the shifter? If not, it could be the shifter hitting the heatshield for the cat.

 

My heatshield is still there but about a week ago I got RT cat put on by Midas crew and they f%$#&* it up the first time they did it.My pipe was turning and hanging close to the ground cause the flanges were spinning.I went there and told them to weld the flange so it wont spin and they finally did it the right way so I don't know if that has to do with anything but I don't know what else. Could it be that I have a loose bolt on the bottom or something ?