My ZTR mower will roll if you push on it even though the dump valves are closed. I checked it with the drive wheels off the ground also. You can easily rotate the wheels by hand. The machine still has enough power to operate, but the left side is stronger than the right. Also it breaks away easily when pointed down hill. This is a real nuisance. It also moves while trailering if there are no straps holding it. I read the owners manual and performed the air bleed procedure, adjusted tracking, and neutral return position. I also checked hydraulic fluid level and saw no air bubbles. There are no abnormal noises coming from the pumps. I have a Wright Sentar with BDP 10L pumps. Machine was a dealer demo. It did this from the time I got it, which was at 72 hours. It now has 200 hours and is getting a little worse.