Diagnosis
Bearing wear in the DC motor or gear train. The 8587w uses a permanent magnet DC motor. As bearings degrade, they produce a high-frequency whine.
How to Fix It
Identify the noise source. With the door disconnected, run the opener. If the whine persists, the issue is internal to the opener. The primary suspect is the motor armature bearings. This requires motor replacement or professional bearing service. Lubrication is not a fix for sealed bearings.
If That Didn't Work
The noise may originate from the gear assembly. Inspect the polymer gear for abnormal wear or missing teeth. A worn gear changes the motor load and can alter the sound.
Heads Up
Do not spray lubricant into the motor vents. This can attract dust and cause electrical shorts. The motor is a sealed unit.