Bought a toro zero turn the other day from a buddy hard up for cash, its a Zmaster z 558 with a 60" deck. Anyways... the left handle makes a horrendous noise when under load, while mowing the other day i lost 95% of my power to the left control. Went home and lifted it with the skidder and it makes no noise at all when i run both the controls. Full of fluid, no leaks, both bypass valves closed. Can't seem to figure this out. Your thoughts??