DIAGNOSIS Bearing failure. Either in the main suction motor or the brush roll motor.
FIX Identify source. Remove brush roll and run vacuum. If whine continues, it's the main motor bearings. If whine stops, it's the brush roll motor bearings. Both require motor unit replacement.
IF THAT DIDN'T WORK Check for a severe air leak. Inspect hose connections, dirt tank seal, and filter seating. A major leak causes high-pitched airflow noise.
HEADS UP Running with clogged filters strains motor bearings. Wash filters monthly.