First thing when I get to about 90mph I hear this sound in the rear as if I'm going over the line on the freeway but it stops once I either let go of the pedal or hit 95mph. What is it? I thought it was the exaust because of the certain vibrations but i figure it would happen if i hit the high rpm in the lower gears. Another problem is when i get to about 110mph it begins to jult as if it loses power? does it need an ecu?