My Bx1800 has a weird problem the dealer has put 50 hours of wrenching time into it and has no idea what is wrong. When the pto is off the tractor does not have any hydrostatic pressure causing the hst to make a grinding sound in forward and reverse. It does not matter if it is in high or low. When this happens the tractor has no power and hardly moves, but if you turn on the pto it runs just fine. Dealer has been scratching their heads over this one. Dealer says the pump has a little wear on it, but nothing critical. Thinks it might be the clutch pack. Any ideas?