I just traded my r1 for 2002 wrx. It has 230k miles. It's a 5 speed. The motor runs fine but after I drive it for 30 mins or so the whole car starts shaking slightly and the transmission makes a grinding noise. If I stop for a second and pull off again it stops. The previous owner said the transmission was just rebuilt a few months ago and he told me about this problem. He said he called a shop and they told him that during the rebuild someone probably put the wrong transmission fluid in it. So when I got it the first thing I did was drain the fluid and put the correct fluid in it. The fluid I put it was a lot thicker than the fluid that came out. I drove it all yesterday and it drove fine. This morning I drove it 15 minutes and it started doing it again any suggestions to what the problem could be?