My transmission

I would say a loose input shaft nut or bad valve body without doing some checking I couldn't tell you for sure. The only problem is if it's the loose input shaft nut to replace it and torque it down it need's a holding tool to hold the first gear clutch pack while you torque the new nut on.I have never tried to do it without the holding tool. You may be able to do hold it with a good strap wrench possibly.