Diagnosis
This is almost always a worn drive belt. The Legacy 920 uses a rubber belt. Noise on ascent means the belt is slipping on the motor pulley or idler pulley due to wear or loss of tension.
How to Fix It
Inspect the entire belt for cracks, glazing, or fraying. Check belt tension. There is an idler pulley assembly with an adjustment bolt. Loosen the locknut and turn the adjustment bolt clockwise to increase tension. Retighten the locknut. Do not overtighten.
If That Didn't Work
The motor pulley itself may be worn smooth. With power disconnected, feel the grooves of the motor drive pulley. If they are polished and shallow, the pulley needs replacement. Belt slippage on a worn pulley causes the noise.
Heads Up
Never lubricate the drive belt. Lubricant will degrade the rubber and cause more slipping. Only lubricate the rail, rollers, and hinges.