hydraulics

IS3100Z--- Right side drive hydraulics making a rapid tapping noise. I can feel the tapping in the hydraulic lines when moving the drive lever forward or back. Tapping changes from one line to the other depending on which way I move the lever. There is no tapping with the lever centered. When first starting the mower, it moves as it should for about a minute, then rapidly goes to not moving the right wheel at all. With the machine off the floor, I can roll the wheel and hear the tapping. There is a lot of "free wheel"(easy roll) back and forth compared to other side. This is a rebuilt wheel motor with 3 hours on it. I purged the right side 3 times to be sure there was no air. Do I have a bad rebuilt wheel motor or is it possibly the pump? Thank you, gregjo1948