grinding noise at 40mph

What is your question?

grinding noise starts at 40 mph when car is cold. tends to jump or car suddenly moves forward after feeling as if it stuck at 20-30mph. once the jump is complete then the grinding may not be heard until 45-50mph. the 'stuck' tendancy is when the car is cold. if i let it warm up for minimum of 5 minutes, it may not 'get stuck' and the grinding does not start til 45-50mph.